Dr. Smiley's phase 3 Chemistry class - chapter 3 midterms review
What does Dalton's atomic theory state?
1) All elements are composed of atoms. 2) All atoms of a given element are identical. 3) Atoms of different elements are different. 4) Compounds consist of the atoms of different elements. 5) Atoms are not created or destroyed in a chemical reaction.
What are some general rules for writing formulas?
1) Each atom present is represented by its element symbol. 2) The number of each type of atom is indicated by a subscript written to the right of the element symbol. 3) When only one atom of a given type is present, the subscript 1 is not written.
What are some physical properties of metals?
1) Efficient conduction of heat and electricity 2) Malleability - can be hammered into thin sheets 3) Ductility - can be pulled into wires 4) A lustrous -shiny - appearance
Explain Dalton's atomic theory
1) Elements are made of tiny particles called atoms. 2) All atoms of a given element are identical. 3) The atoms of a given element are different from those of any other element. 4) Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms. 5) Atoms are indivisible in chemical processes. That is, atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together. Dalton's model successfully explained important observations such as the law of constant composition. This law makes sense because if a compound always contains the same relative numbers of atoms, it will always contain the same proportions by mass of the various elements.
Law of constant composition
A given compound always contains elements in exactly the same proportion by mass.
As scientists of the eighteenth century studied the nature of materials, several things became clear, what are they?
1. Most natural materials are mixtures of pure substances. 2. Pure substances are either elements or combinations of elements called compounds. 3. A given compound always contains the same proportions (by mass) of the elements. This principle became known as the law of constant composition. It means that a given compound always has the same composition, regardless of where it comes from.
Periodic table
A chart showing all the elements arranged in columns in such a way that all the elements in a given column exhibit similar chemical properties.
What is an important fact to remember?
A chemical compound must have a net charge of zero. This fact means that if a compound contains ions, then: Both positive ions -cations and negative ions - anions - must be present. The numbers of cations and anions must be such that the net charge is zero.
Ionic compound
A compound that results when a metal reacts with a nonmetal to form cations and anions.
Nuclear atom
A concept of the atom as having a dense center of positive charge (the nucleus) surrounded by moving electrons.
What does the law of constant composition state?
A given compound always contains the same proportion by mass of the elements of which it is composed.
Explain Transition metals
A large collection of elements that spans many vertical columns consists of the transition metals.
Diatomic molecules
A molecule composed of two atoms.
What does each element have?
A name and a symbol: The symbol usually consists of the first one or two letters of the element's name. Sometimes the symbol is taken from the element's original Latin or Greek name.
Anion
A negatively charged ion.
Electrons
A negatively charged subatomic particle.
Cation
A positively charged ion.
Proton
A positively charged subatomic particle located in the atomic nucleus.
Chemical formula
A representation of a molecule in which the symbols for the elements are used to indicate the types of atoms present and subscripts are used to show the relative numbers of atoms.
Explain a cathode ray tube:
A stream of electrons passes between the electrodes. The fast-moving particles excite the gas in the tube, causing a glow between the plates.
Neutron
A subatomic particle in the atomic nucleus with no charge.
Compound
A substance made of two or more different elements joined together in a specific way.
Robert Boyle's definition of the term element was based on experiments. What was it?
A substance was an element unless it could be broken down into two or more simpler substances.
Dalton's atomic theory
A theory established by John Dalton in the early 1800s, used to explain the nature of materials.
Groups
A vertical column of elements on the periodic table.
Complete the sentence: Note that...
All Group 7 atoms gain one electron to form 1- ions and that all nonmetals in Group 6 gain two electrons to form 2- ions.
What does the periodic table show?
All of the known elements in order of increasing atomic number; the table is organized to group elements with similar properties in vertical columns.
What is the formula for the binary ionic compound made from the following ions: Al³⁺ and O²⁻
Al₂O₃
Ion
An atom or a group of atoms that has a positive or negative charge.
Briefly explain the nature of electric currents.
An electric current can travel along a metal wire because electrons are free to move through the wire; the moving electrons carry the current. In ionic substances, the ions carry the current. Therefore, substances that contain ions can conduct an electric current only if the ions can move—the current travels by the movement of the charged ions.
Nonmetals
An element that does not exhibit metallic characteristics. Chemically, a typical nonmetal accepts electrons from a metal.
Metalloids
An element that has both metallic and nonmetallic properties.
Complete the sentence: Nonmetals generally lack those properties that characterize metals...
And show much more variation in their properties than metals do.
At present, about how many elements are known, and how many of them occur naturally?
At present, about 115 different elements are known, 88 of which occur naturally.
Complete the sentence: The number of electrons a given atom possesses greatly affects the way it can interact with other atoms. As a result...
Atoms of different elements, which have different numbers of electrons, show different chemical behaviors.
What are isotopes?
Atoms with the same number of protons but a different number of neutrons.
Isotopes
Atoms with the same number of protons but different numbers of neutrons.
Finish the sentence: Many scientists pondered the nature of the atom during the 1800s...
But it was not until almost 1900 that convincing evidence became available to show that the atom has a number of different parts.
How is a compound represented?
By a chemical formula in which the number and type of atoms present are shown by using the element symbols and subscripts.
The Greeks were the first to try to explain why chemical changes occur.
By about 400 b.c. they had proposed that all matter was composed of four fundamental substances: fire, earth, water, and air.
How can atoms form ions?
By gaining or losing electrons: Metals tend to lose one or more electrons to form positive ions called cations; these are generally named by using the name of the parent atom. Nonmetals tend to gain one or more electrons to form negative ions called anions; these are named by using the root of the atom name followed by the suffix -ide.
How can we produce a charged entity called an ion?
By taking a neutral atom and adding or removing one or more electrons.
How is an anion named?
By taking the root name of the atom and changing the ending. By adding -ide to the root of the atom name.
How do we recognize substances that contain ions?
By their characteristic properties. They often have very high melting points, and they conduct an electric current when melted or dissolved in water.
What is the most important element?
Carbon - which is found in virtually all of the molecules that make up the living cell.
Complete the sentence: All of the materials in the universe can be...
Chemically broken down into about 100 different elements.
What is the abbreviation system for naming chemicals?
Chemists have invented a set of abbreviations or element symbols for the chemical elements. These symbols usually consist of the first letter or the first two letters of the element names. The first letter is always capitalized, and the second is not. Sometimes, however, the two letters used are not the first two letters in the name.
What do ions combine to form?
Compounds.
How can you visualize how small the nucleus is compared with the size of the atom?
Consider that if the nucleus were the size of a grape, the electrons would be about one mile away on average.
Although Dalton's model was not accepted immediately, what did he do?
Dalton was convinced that he was right and used his model to predict how a given pair of elements might combine to form more than one compound. He pictured compounds as collections of atoms. When the existence of these substances was verified, it was a triumph for Dalton's model. Because Dalton was able to predict correctly the formation of multiple compounds between two elements, his atomic theory became widely accepted.
What do all of the elemental forms of the Group 7 (Halogens) contain?
Diatomic molecules.
The subatomic particle that determines an element's chemical properties is the __________.
Electrons.
What are metalloids?
Elements that have some metallic and some nonmetallic properties.
Complete the sentence: Some elements found in the body - called trace elements - are crucial for life...
Even though they are present in relatively small amounts.
True or false: Most elements are un-reactive.
False - most elements are reactive. Their atoms tend to combine with those of other elements to form compounds quite readily.
True or false: Dalton's model was accepted immediately in society.
False. Like most new ideas, Dalton's model was not accepted immediately.
True or false: Metals always form negative ions.
False. Metals always form positive ions. This tendency to lose electrons is a fundamental characteristic of metals.
True or false: Isolated atoms do form ions on their own
False. They do not form ions on their own.
How can the ion that a particular atom will form be predicted?
From the atom's position on the periodic table: Elements in Group 1 and 2 form 1+ and 2+ ions, respectively. Group 7 atoms form anions with 1- charges. Group 6 atoms form anions with 2- charges.
What did Rutherford conclude about the plum pudding model from his findings?
From these results, he concluded that the plum pudding model for the atom could not be correct. The large deflections of the alpha particles could be caused only by a center of concentrated positive charge that would repel the positively charged alpha particles. Most of the alpha particles passed directly through the foil because the atom is mostly open space. The deflected alpha particles were those that had a "close encounter" with the positive center of the atom, and the few reflected alpha particles were those that scored a "direct hit" on the positive center. In Rutherford's mind, these results could be explained only in terms of a nuclear atom - an atom with a dense center of positive charge- the nucleus - around which tiny electrons moved in a space that was otherwise empty.
How are groups often referred?
Groups are often referred to by the number over the column.
What did J.J. Thomson conclude?
He concluded that the atom must also contain positive particles that balance exactly the negative charge carried by the electrons, giving the atom a zero overall charge.
Who is Robert Boyle?
He is best known for his pioneering work on the properties of gases, but Boyle's most important contribution to science was probably his insistence that science should be firmly grounded in experiments.
Give some examples of elements that exist as diatomic molecules.
Hydrogen, nitrogen, and oxygen.
Provide some examples of elements that exist as diatomic molecules in their elemental form
Hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, iodine.
What did Rutherford and his co-worker discover?
In 1932 Rutherford and a coworker, James Chadwick, were able to show that most nuclei also contain a neutral particle that they named the neutron. A neutron is slightly more massive than a proton but has no charge.
Compound
In light of Dalton's atomic theory, this statement simply means that a compound always contains the same relative numbers of atoms of each element.
Who was John Dalton?
In the early 1800s, he offered an explanation for them that became known as Dalton's atomic theory. Dalton was an English scientist who made his living as a teacher in Manchester. Although Dalton is best known for his atomic theory, he made contributions in many other areas, including meteorology (he recorded daily weather conditions for 46 years, producing a total of 200,000 data entries). A rather shy man, Dalton was color-blind to red (a special handicap for a chemist) and suffered from lead poisoning contracted from drinking substances that had been drawn through lead pipes.
Explain J.J. Thomson
In the late 1890s, a British physicist named J. J. Thomson used a cathode ray tube - Fig. 3.1 - to show that the atoms of any element can be made to emit tiny negative particles. - He knew they had a negative charge because he could show that they were repelled by the negative part of an electric field. - Thus he concluded that all types of atoms must contain these negative particles, which are now called electrons.
Complete the sentence: As we have noted, the matter around us consists mainly of mixtures. Most often these mixtures contain compounds...
In which atoms from different elements are bound together.
What do many substances contain?
Ions. In fact, whenever a compound forms between a metal and a nonmetal, it can be expected to contain ions. We call these substances ionic compounds.
Complete the sentence: The list of elements found in living matter...
Is very different from that for the earth's crust.
What is the simplest view of the atom?
It consists of a tiny nucleus - about 10⁻¹³ cm in diameter - and electrons that move about the nucleus at an average distance of about 10⁻⁸ cm from it.
Complete the sentence: Although the atoms of different elements also differ in their numbers of protons...
It is the number of electrons that really determines chemical behavior.
What does it mean to say that compounds are electrically neutral?
It means that the sum of the charges on the anions and cations in the compound must equal zero.
Complete the sentence: Compounds are made by combining atoms of the various elements...
Just as words are constructed from the 26 letters of the alphabet.
Complete the sentence: Whereas almost all metals are solids at normal temperatures...
Many nonmetals - such as nitrogen, oxygen, chlorine, and neon - are gaseous, and one - bromine - is a liquid. Several nonmetals - such as carbon, phosphorus, and sulfur - are also solids.
What type of properties do most elements have?
Metallic properties - the metals - and appear on the left side of the periodic table.
What is the formula for the binary ionic compound made from the following ions: Mg²⁺ and S²⁻
MgS
Complete the sentence: In contrast to the Group 1, 2, and 3 metals...
Most of the transition metals form cations with various positive charges. For these elements, there is no easy way to predict the charge of the cation that will be formed.
What is the formula for the binary ionic compound made from the following ions: Na⁺ and Cl⁻
NaCl.
How many elements account for about 98% of the earth's crust, oceans, and atmosphere?
Nine.
The Periodic table
Note that each box of this table contains a number written over one or two letters.
The Periodic Table
Note that the elements are listed on the periodic table in order of increasing atomic number. They are also arranged in specific horizontal rows and vertical columns.
The Periodic Table
Notice that elements 112 through 115 have unusual three-letter designations beginning with U. These are abbreviations for the systematic names of the atomic numbers of these elements. "Regular" names for these elements will be chosen eventually by the scientific community.
Explain Rutherford's experiment
One of his main areas of interest involved alpha particles, positively charged particles with a mass approximately 7500 times that of an electron. In studying the flight of these particles through air, Rutherford found that some of the alpha particles were deflected by something in the air. Puzzled by this observation, he designed an experiment that involved directing alpha particles toward a thin metal foil. Surrounding the foil was a detector coated with a substance that produced tiny flashes wherever it was hit by an alpha particle. The results of the experiment were very different from those Rutherford anticipated. Although most of the alpha particles passed straight through the foil, some of them were deflected at large angles, and some were reflected backward. This outcome was a great surprise to Rutherford - he described it as comparable to shooting a gun at a piece of paper and having the bullet bounce back. Rutherford knew that if the plum pudding model of the atom were correct, the massive alpha particles would crash through the thin foil like cannonballs through paper. So he expected the alpha particles to travel through the foil experiencing, at most, very minor deflections of their paths.
Explain the Plum Pudding model in simpler terms
One of the early models of the atom was the plum pudding model, in which the electrons were pictured as embedded in a positively charged spherical cloud, much as raisins are distributed in an old-fashioned plum pudding.
What are the most abundant elements in the human body?
Oxygen, carbon, hydrogen, and nitrogen.
What forms the basis for all biologically important molecules?
Oxygen. carbon, hydrogen, and nitrogen.
Complete the sentence: The subatomic particles that contribute most to an elements mass are ________ and _________.
Protons and neutrons.
Complete the sentence: We have seen that an atom has a certain number of...
Protons in its nucleus and an equal number of electrons in the space around the nucleus. This results in an exact balance of positive and negative charges.
What does the nucleus contain?
Protons, which have a positive charge equal in magnitude to the electrons' negative charge, and neutrons, which have almost the same mass as protons but no charge.
What did Rutherford initially conclude?
Rutherford concluded that the nucleus must have a positive charge to balance the negative charge of the electrons and that the nucleus must be small and dense. By 1919 Rutherford had concluded that the nucleus of an atom contained what he called protons. A proton has the same magnitude - size - of charge as the electron, but its charge is positive. Rutherford reasoned that the hydrogen atom has a single proton at its center and one electron moving through space at a relatively large distance from the proton - the hydrogen nucleus. He also reasoned that other atoms must have nuclei - the plural of nucleus - composed of many protons bound together in some way.
Explain Ernest Rutherford:
Rutherford was born on a farm in New Zealand. In 1895 he placed second in a scholarship competition to attend Cambridge University, but he was awarded the scholarship when the winner decided to stay home and get married. Rutherford was an intense, hard-driving person who became a master at designing just the right experiment to test a given idea. He was awarded the Nobel Prize in chemistry in 1908.
What did scientists come to think due to Dalton's atomic theory?
Scientists came to believe that elements consist of atoms and that compounds are a specific collection of atoms bound together in some way.
Transition metals
Several series of elements in which inner orbitals - d or f orbitals - are being filled.
Complete the sentence: Nature often uses a relatively...
Small number of fundamental units to assemble even extremely complex materials.
The next 2000 years of chemical history - after the Greeks - were dominated by alchemy.
Some alchemists were mystics and fakes who were obsessed with the idea of turning cheap metals into gold. However, many alchemists were sincere scientists, and this period saw important events: the elements mercury, sulfur, and antimony were discovered, and alchemists learned how to prepare acids.
Complete the sentence: Given J. J. Thomson's results, it was natural to wonder what the atom might look like. J. J. Thomson and William Thomson - better known as Lord Kelvin, and no relation to J. J. - are credited with proposing that the atom...
Something like plum pudding - a pudding with raisins randomly distributed throughout. They reasoned that the atom might be thought of as a uniform "pudding" of positive charge with enough negative electrons scattered within to counterbalance that positive charge.
What are ions?
Species with a charge.
Complete the sentence: You can always determine the number of neutrons present in a given atom by...
Subtracting the atomic number from the mass number.
What did experiments by J.J. Thomson and Ernest Rutherford show?
That atoms have internal structure: 1) The nucleus, which is at the center of the atom, contains protons (positively charged) and neutrons (uncharged). 2) Electrons move around the nucleus. -Electrons have a small mass : 1 / 1836 of the proton mass. -Electrons have a negative charge equal and opposite to that of the proton.
Alkali metals
The Group 1 metals.
Alkaline earth metals
The Group 2 metals.
Halogens
The Group 7 elements.
Noble gases
The Group 8 elements.
What happens to an atom when electrons are added to it?
The atom becomes much larger.
Complete the sentence: In a chemical formula...
The atoms are indicated by the element symbols and the number of each type of atom is indicated by a subscript, a number that appears to the right of and below the symbol for the element.
Explain the elements that lie close to the "stair-step" line
The elements that lie close to the "stair-step" line often show a mixture of metallic and nonmetallic properties. These elements, which are called metalloids or semimetals, include silicon, germanium, arsenic, antimony, and tellurium.
Who first arranged the periodic table?
The elements were first arranged in this way in 1869 by Dmitri Mendeleev, a Russian scientist. Mendeleev arranged the elements in this way because of similarities in the chemical properties of various "families" of elements.
Atoms
The fundamental unit of which elements are composed.
The Periodic Table
The letters are the symbols for the elements.
What happened as Boyle's experimental definition of an element became generally accepted?
The list of known elements grew and the Greek system of four elements died.
Explain the origins of the names of the chemical elements.
The names of the chemical elements have come from many sources. Sometimes the names come from descriptions of the element's properties, sometimes the name reflects the place where the element was discovered, and sometimes the name honors a famous scientist.
How are ions formed?
When metallic elements combine with nonmetallic elements.
How can we produce a positively charged ion called a cation?
When one or more electrons are lost from a neutral atom.
Atomic number
The number of protons in the nucleus of a given atom.
The Periodic Table
The number shown above each symbol is the atomic number - the number of protons and also the number of electrons - for that element.
A cation is named using the name of the what atom?
The parent atom.
Nucleus
The relatively small, dense center of positive charge in an atom.
Which side does the nonmetals appear on in the periodic table?
The right side.
Mass number
The total number of protons and neutrons in the nucleus of a given atom.
What is important to recognize about ions?
They are always formed by removing electrons from an atom - to form cations - or adding electrons to an atom - to form anions. They are never formed by changing the number of protons in an atom's nucleus.
What does the name "periodic table" refer to?
Thus the name periodic table refers to the fact that as we increase the atomic numbers, every so often an element occurs with properties similar to those of an earlier - lower-atomic-number -, element. For example, the elements shown vertically below all show similar chemical behavior and so are listed vertically, as a "family" of elements.
What is true for any ionic compound?
Total charge of cations + Total charge of anions = Zero net charge.
True or false: Most of the elements are metals
True.
True or false: Nonmetals form negative ions by gaining electrons.
True.
True or false: Some atoms lose more than one electron.
True.
True or false: The structures of solid nonmetallic elements are more varied than those of metals
True. In fact, different forms of the same element often occur.
Complete the sentence: Because the atoms of these Group 8 elements do not combine readily with those of other elements...
We call them the noble gases.
What can we say about an atom?
We say that an atom is a neutral entity—it has zero net charge.
Complete the sentence: Most elements are quite reactive: Their atoms tend to combine with those of other elements to form compounds quite readily. As a result...
Wee do not often find elements in nature in pure form—uncombined with other elements. However, there are notable exceptions.
Explain the significance of James Chadwick.
When Dalton stated his atomic theory in the early 1800s, he assumed that all of the atoms of a given element were identical. This idea persisted for more than 100 years until James Chadwick discovered that the nuclei of most atoms contain neutrons as well as protons. After the discovery of the neutron, Dalton's statement that all atoms of a given element are identical had to be changed to: "All atoms of the same element contain the same number of protons and electrons, but atoms of a given element may have different numbers of neutrons."
How can we produce a negatively charged ion called an anion?
When a neutral atom gains electrons.
Complete the sentence: Note that...
the Group 1 metals all form 1+ ions , the Group 2 metals all form 2+ ions , and the Group 3 metals form 3+ ions. Therefore, for Groups 1 through 3, the charges of the cations formed are identical to the group numbers.
