chemistry chapter 2

Naming bases-

A base can be described as a substance that yields hydroxide ions(OH-) when dissolved in water. Examples are NaOH-Sodium hydroxide KOH-Potassium hydroxide Ammonia(NH3) is a molecular compound in a gaseous or pure liquid state, that is classified as a common base. When it reacts with water OH- is produced.

Diatomic molecule

A hydrogen molecule is a diatomic molecule because it contains only two atoms. Other elements that normally exst as diatomic molecles are nitrogen, oxygen, fluorine, chlorine, bromine, iodine. A diatomic molecule can also contain atoms of different elements such as hydrogen chloride(HCI) and carbon monoxide(CO)

Molecules

A molecule is an aggregate of at least two atoms in a definite arrangement held together by chemical forces also called chemical bonds. A molecule may contain aoms of the same elemnt or atoms of two or more element joined ina fixed ratio, in acordinace with the law of definite proportions. This a molecule is not necessarily a compound, which by definition is made up of two or more elements.

Atomic number-

All atoms can be identified by the number of protons in the nucleus of each atom of an element is called the atomic number. In the neutral atom, the number f protons are equal to the number of electrons, so the atomic number also indivates the number of electrons present in an atom. The chemical identity of an atom can be determined solely bu its atomic number. For example, the atom number of nitrogen is 7; this means that each neutral nitrogen has 7 protons and 7 electrons. Every atom in the universe contains 7 protons is correctly named nitrogen

Acid

An acid can be described as a substance that yields hydrogen ions(H+) when dissolved in water. Formula for acids contain one or more hydrogen atoms as well as an anionic groups. Anions whose names end in "ide" have associated acids with a "hydro" prefix and "ic" ending. In some cases, HCI is known as both hydrogen and chloride and hydrochloric acid. The name for this compou d depends on the physical state. In he gaseous or pure liguid state, HCI is a molecular compound called hydrogen chloride. When dissolved in water, the molecules break up into H+ and CI_ ions, in this condition the substance is called hydrochloric acid.

1. Argue how one of Dalton's hypotheses is another way of stating the law of conservation of mass.

Daltons fourth hypothesis is another way of stating law of convervation of mass, which is the fact that matter cannot be created or destroyed. Because matter is made of atoms that are unchanged in a chemical reaction, it follows that mass mus be unchanged as well.

Binary compounds-

Many ionic compounds are binary compounds, or compounds formed from just two elements. For binary ionic compounds the first element namd is the metal cation followed by the nometallic anion. Thus NACI os sodium chloride. The anion is named by taking the first part of the element name(clorine) and adding "ide". Potassium bromine(KBr), zinc iodide(ZNI2) are also binary compounds. The "ide" ending is also used for certainanion groups containing different elements such as hydroxide(OH-). Thus compound, LiOH is lithium hydroxide.

Periodic table

Recognitions of periodic regularities in physical and chemical behavior and the need to organized the large volume of available information about the structure and properties of elemental substances led to the development of the periodic table-a chart in which elements having similar chemical and physical properties are grouped together. The modern periodic table shows that elements are arranged by atomic number in horizontal rows called periods and vertical columns known as groups or families, according to similarities in their chemical properties. All halogens are diatomic naturally. most of evrything is monotomic.

1. Discuss how the neutron was discovered.

Rutherford has a problem unsolved because it was known that hydrogens the simplest atom has one proton and helium atom has two protons. The ration of heium to hydrogen should be 2:1, howevr it is 4:1/ rutherfordand others proposed that there must be another type of subatomic particle in the nuceleus which was proof by james chadwhich. When he bombarded a thin sheet of beryllium with alpha aprticles, a very higher enrgy radiation similar t y rays were emitted by th metal. Later epxeriments showed that the rays actually consisted of electrically neutral particles javing a mass slightly greather than that of protos. He named the particles neutrons. The mystery of mass ratio can be explained. In helium nucleus, there are two protons and twn neutrons but in hydrogen nucelsu there is one protona d no netruons therefore ratio is 4:1.

Empirical formula:

Thus the empirical formula tells us which elements are present and the simplest whole number ratio of their atoms but not necessarily the actual number in a molecule. They are written by reducing the subscripts in moecl formilas to the smallest possible hole numbers. Molecular formulas are the true formulas of the molecules. Molecular formula: N2H4 Empirical formula:NH2

Molecular compounds-

Unlike ionic compounds, molecular compounds have descrete molecular units. They are usually composed of nometallic elements. Many molecular compounds are binary compounds. Naming binary compounds is similar to naming binary ionic compounds. We place the name of the first element in the formula, first the second element is named by adding "ide"" to the root of the element name. It is common for one pair of elements to form several compounds. Confusing is avoided by the use of greek prefixes to denote the number of atoms in each element.

Oxacid-

-Oxoacids are acids that contain hydrogen, oxygen, and another element(the central element) The formulas of oxoacids are usually written with H first, followed by the central element then O. H2CO3-Carbonic acid Often two or more oxoacids have the same central atom but a different number of O atoms 1. Addition of one O atom to the "ic" acid: The acid is called "per...ic" acid. Thus adding an O atom to HCIO3 changes chloric acid to perchloric acid, HCIO4 2. Removal of one O atom from "ic" acid: The acid is called "ous" acid.Thus nitric acid, HNO3, becomes nitrous acid, HNO2 3. Removal of two O atoms from "ic" acid: The acid is called "hypo....-ous" acid. Thus, when HBr O3 is converted to HBrO, the acid is called hypobromous acid.

Oxoanions

-anion containing one or more oxygen atoms bonded to another element 1. When all H ions are removed from the "ic" acid, the anions named ends with "ate." For example, the anion CO32- derived from H2CO3 is called carbonate. 2. When all the H ions are removed from the "ous" aid, the anion's name ends with "ite:.This, the anion CIO2- derived from HCIO2 is called chlorite 3. The names of anions in which one or more but not all of the hydrogenen ions have been removed must indicte the number of H ions present. For example, consider the anions derived from phosphoric acid: H3PO4 Phosphoric acid H2PO4 Dihydrogen phosphate HPO42- Hydrogen phosphate PO43- Phosphate Note we usually moit the prefix mono when there is only one H in the anion.

Millakans oil drop experiment

An experiment performed by Robert Millikan in 1909 determined the size of the charge on an electron. He also determined that there was a smallest 'unit' charge, or that charge is 'quantized'. He received the Nobel Prize for his work. We're going to explain that experiment here, and show how Millikan was able to determine the size of a charge on a single electron. What Millikan did was to put a charge on a tiny drop of oil, and measure how strong an applied electric field had to be in order to stop the oil drop from falling. Since he was able to work out the mass of the oil drop, and he could calculate the force of gravity on one drop, he could then determine the electric charge that the drop must have. By varying the charge on different drops, he noticed that the charge was always a multiple of -1.6 x 10 -19 C, the charge on a single electron. This meant that it was electrons carrying this unit charge.

ion

An ion is an atom or a group of atoms that have a net positive or negative charge. The number of positively charged protons in the nucleus of an atom remains the same during ordinary chemical changes(called chemical reactions), but negatively charged electrons may be lost or gained. The loss of one or more electrons from a netrual atom results in a cation, an ion with a net positive charge. A sodium atom can readily lose an electron to become sodium cation which is represented by Na+. On the other hand, an anion is an ion whose net charge is negative due to an increase in the number of electrons. A chlorine atom(CI) can gain an electron to become chloride ion(CI-). Monotomic ions contain only one atoms(Na+, CI-). With very few exceptions, metals tend to form cations and nonmetals form anions. Two or more molecules can combine to form an ion that has a net positive charge or net negative charge. These are polyatomic ions. Polyatomic ions are OH-(hydroxide ion) or CN- ion.

1. Define the term "isotope" and be able to identify the differences between the isotopes of a given element.

Atoms that have the same atomic number but different mass numbers are called isotopes. Atoms have a different number of neutrons. The accepted way to denote the atomic number and mass number of an atom of element X is as follows: With the exception of hydrigen, isotopes of elements are identifid by their mass numers. The chemical protopertoes of an element are determined primarily by the protons and electrons in itd atoms; neutroms do not take part in chemical changes under normal conditions. Therefore, isotopes of th same element have similar chemistries, forming he same types of compouhds ajd similar reactivities.

rutherfords experiment

He used alpha particles which consisted of positively charged particles. He carried out many experiment susing thin foil of gold and other metals as targets for alpha particles from radioactive source. They observed that a majority of particles penentrated the foil either deflected or only withslight deflection. He was surprised the alpha particles were so spreaded out that they were xpected to diffuse across the foil with little deflection. He then devised a new model of atomic structure, suggesting that the atom must be empty soace. The structure would allow most alpha particles to pass through the gold foil with little or no deflection. Hethen made a new model suggesin g that the atom is emptyspace and the structure allow most of the a particles to pass through the gold foil with little or no deflection. Thr atoms positive charges, are all concentrated in the nucleus, a dense core of the atom. He then defised a new atom srcutre, suggesting that most of the batom is empty space. Thisw would allow alpha partice;s to pass through the dold with little or no defelectin. Moreoveran alpha aprticle traveling toward a nucleus would experience big repulsion that can reverse direction of the mowing particle. The positively charged atoms in the nucelsu are called protons. The charge of each proton haa the same magneitde of that as an elextron as foubd. The mass is about 1840 times the mass of the electron.

Thompson experiment

In a series of investigations, there were experiments which demonstrated that atoms are made up of smaller particulars which are subatomic particles. This research lead to discovering electrons, protons, and neutrons. In 1860s, scientist studied radiation, the emission and transmission of energy through space in the form of waves. There was a glass tube, which most air was evaculated. When the two metal plates are connected to a high-voltage source, the negatively charged plate called the cathode emits inviable ray. The cathode ray is drawn to positively charged plate, the anode, where it passes through a hole and continues traveling to the other end of the tube. When the ray strikes the specifically coated suface, it produces a strong flourescnece, or bright light. In 1900s, it has came clear that atoms contain electrons and are electrically neutral. To maintain the neutrality, an atom must contain an equal number of positive and negative charges. On basis of this information, Thomson proposed that an atom could be thought as a uniform, positive sphere of matter which electrons are embedded. Thomsons so called "plum pudding" model was accepted in the theory.

Three categories of elements-

The elements can be divided into three categories, mentals, nonmentals, and metalloids. A metal is a good conductor of heat and electricity, whereas a nometal is usually a poor conductor of heat and electricity, A metalloid has properties that are intermediate between those of metals and nonmentals. A majority of known elements are metalsm only seventeen are nonmetals, and eight elements are metalloids. From left to right across any period, the physical and chemical properties of elements change gradually from metallic to nonmetallic. Elements are often referred to collectively by their periodic table group number. Group 1: alkali metals Group 2: alkaline earth metals Group 17: halogens Group 18: noble or rare gases

Formulas of ionic compounds-

The formulas of ionic compounds are usually the same as their empirical formulas because ionic compounds do not consist of discrete molecular units. In order for ionic compounds to be electrically neutral, the sum of charges on the cation and anion in each formula unit must be zero. If the charges on the cation and anion are numerically different, we apply the formula electrically neutral: h subscript of the cation is numerically equal t the charge in the anion and the subscript of the anion is numericallu equal to the charge on the cation. If the charges are numerically equal, then no subscripts are necessary. • Potassium Bromide. The potassium cation K+ and bromine anion Br- combine to form the ionic compound potassium bromide. The sum of the chargers is +1 +(-1)=0, so no subscripts are necessary. The formula is KBr. • Zinc Iodide. The zinc cation Zn2+ and the iodine anio I- combine to form zinc iodie. The sum of the charges of one Zn2+ ion and one I- one is +2 +(-1)=+1. To make the charges add up to 0 we multiple the -1 charge of the anion by 2 and add the subscript 2 to the symbol iodine, there, the formula of zinc iodide is ZnI2 Aluminum Oxide. The cation Al3+ and the oxygen anion is O2-.

Introduction to organic compounds-

The simplest type of organic compounds is the hydrocarbons, which contain carbon and hydrogen atoms. They are used for fuels for domestic and industriel heating, generating electrcitiy, powering internal combustion engines, and starting materials for chemical industry. One class of hydrocarbons is called alkanes. The straight chain alkakes, are where the carbon atoms have no branches and are in a chain. The chemistry of organic compounds is determined by the functional groups, which consist of one or a few atoms bonded in a specific way. The chemical properties of these molecus can be predicted based on the reactivity of the functional groups.

Polyatomic molecules-

The vast majority of molecles contained more than two atoms. They can be atoms of the same element such as Ozone(O3), which is made up of three atoms of oxygen or they an be combinations of two or more different elements. Molecules containing more than two atoms are polyatomic molecules. Like ozone, water and ammonia(NH3) are polyatomic molecules.

Hydrates-

These are compounds that have a specific number of water molecules attatched to them. For example, in its normal state, each unit of copper(i) sulfate has five water molecules associated with it. The systematic name is copper(II) sulfate pentahydrate, and its formula is written as CuSO4 x 5H2O. the water molecules can be driven off by heating. When this occurs, the resulting compound is CuSO4, which is sometimes anhydrous copper(II) sulfate; anyhdyrous" means tha the compound no longer has water moleces associated with it. Another hydrate is BaCI2 x 2H2O barium chloride dehydrate

Terinary compounds-

These compounds consists of three or more elements. Certain metals, especially tramsition metals can form more than one type of cation. LIOH-terinary compound. The accepted procedure for designinating different cations of the same element is to use roman numerals. I is usedfor one positive charge, II is used for two positive charge and so on,.

Law of multiple proportions-

if two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers. In short, compounds differ in the number of atoms of each kind that combine. For example, carbon forms two stable compounds with oxygen, mainly carbon monoxide and carbon monoxide. The counpounds are different in the number of atoms each kind can combined. Modern measurement techniques indicate that one atom of carbn combines with one of ocygen in carbon monoxide and the one atom of carbon combines two oxygen atoms in carbon dioxide. This the ratio of oxygen in carbon monoxide to oxygen in carbon dioxide is 1:2. This result is consistent with the law of multiple proportions because the mass of an element in a compound is proportional to the number of atoms each element presents.

greek prefixes

mono-1 di-2 tri-3 tetra-4 penta-5 hexa-6 hepta-7 octa-8 nona-9 deca-10

Recall from memory the names for the three isotopes of hydrogen.

protium-1 mass number, 1 atomic number deuterium-2 mass number, 1 atomic number Tritium-3 mass number, 1 atomic number

Molecular formula-

shows the exact number of atoms of each element in the smallest unit of a substance. The subscript represents the number of atoms present. O3 and O2 are allotropes. An allotrope is one of two or more disctinct forms of an element. Two standard types of molecular models are ball-and-stick models and space-filling models. Space filling models are more accurate since they show variations of atoms in atomic size.

Law of definite proportions

states that different samples of the same compound always contain its constituent elements in the same proportion by mass. In each sample of carbon diocide obtained fromm different sources, we would find the ratio of masses of carbon and oxygens the same

Chemical formula-

t is used to express the composition of molecles and ionic compounds in terms of chemical symbols

Mass number

the mass number is the total number of neutrons and protons present in the nucleus of an atom of an element. Except for the most common form of hydrogen, which has one proton and no neutrons, all atomic nuclei contains both protons and neutrons. Mass number=number of protons+number of neutrons =atomic number + number of neutrons

1. Restate the points of Dalton's atomic theory.

• Elements are composed of very small particles called atoms. On the basis of this, an atom is a basic unit of an element that can enter into chemical combination. • All atoms of an element are identical, having the same sixe, mass, and chemical properties. The atoms of one element are different from the atoms of other elements. • Compound are composed of atoms of more than one element. In any compound, the ratio of the numbers of atoms of any two elemnts present is either an interger or simple fraction A chemical reaction involves only the separation, combination, or rearrangement of atoms; it does not result in their creation or destruction

Guidelines for naming compounds with prefixes:

• The prefix "mono" may be omitted for the first element. For example, PCI3 is named phosphorus trichloride not monophosphorous trichloride. Thus the absence of the prefix for the first element usually means that only one atom of that element is present in the molecule. • For oxides, the ending "a" in the prefix is sometimes omitted. For example, N2O4 may be called dinitrogen tetroxide rather than dinitrogen tretraoxide. • Exceptions to the use of greek prefixes are molecular compounds that contain hydrogen. Traidionally, many of these compounds are called either by their common, nonsystematic names or names that do not indicate specifcallt the number of H atoms present: B2H6-diborane. The order of writing the elemtns in the formulas is irregular. These examples show that H is written first in water and ydrogen sulfide, whereas H is written last in the other compounds.