chemisty c2
carbon-12 is the standard on the atomic mass table
unform massscale the most abundant isotope of carbon, carbon-12 reference one atom of this isotope is 12 units of mass (atomic mass units)(amu)(u) the size of a single amu us established to be 1/12 of the mass of a single carbon 12 atom if an average atom of an element has a mass twice of a c12 its would be 24u!
ionic compounds
under appropriate conditions, electrons are able to transfer between one another. formation of ions in salt results from transfer of electrons. each sodium game one electron to each chlorine. ionic compound - made of two charged ions ionic compounds are made when metals react with nonmetals. not always gaining or losing just ONE electron. safe to say one oxygen belongs to two hydrogen because molecules don't exist in ionic compounds, the subscripts are always chosen to speify the smallest whole number tail of ions we take the smallest unit of an ionic compound to be whatever is represented in its formula and call this unit a formula unit.
his theory
- easily explained the law of conservation of mass. - according to theory, a chemical reaction is simply a recordering of atoms from one combination to another. if no atoms are gained or lost and if the masses of the atoms can't change, then the ,ass after the reaction must be ame - law of definite also easy to explain. his theory says a given compound always as atoms in same ratio. suppose there are two elements A and B. if the mass of B is twice that of A atom than the mass ratio is that.
atomic theory led to discovery of multiple proportions
- support for dalton's came when other scientists studied elements that are able to combine to give two o more compounds. - sample sizes are not the same, each has same mass of sulfur and ratios
why c12?
1. carbon is a very common element 2. by choosing this, the atomic masses of nearly all other elements are almost whole numbers with the lightest atom hydrogen having a mass of 1amu.
DALTON'S ATOMIC THEORY
1. matter consists of tiny particles called atoms 2. atoms are indestructible. in chemical reactions, the atoms rearrange but they themselves do not break apart. 3. in any sample of a pure element, all the atoms are identical in mass and other proportions 4. the atoms of difference elements differ in mass and other proportions 5. when atoms of different elements combine to form compounds new and more complex particles form however, in a given compound the constant atoms are always present in the same fixed numerical ratio.
DIATOMIC MOLECULE ELEMENTS NATURAL
Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Bromine, Iodine,
METALS. Group IA - Metals
METALS. Group IA - Metals form compounds with oxygen that dissolve in water to give solutions that are strongly alkaline or caustic. Also, called alkali metals
cont.
SAME ELECTRICAL CHARGE - REPEL DIFFERENT CHARGE - ATTRACT THIS CHARGE holds electrons to nucleus neutrons have no charge and are said to be NEUTRAL ELECTRONS REPEL EACH OTHER, keep them spread out BALANCES of attract and repel controls size of atom protons also repel each other . stay together in small volume of nucleus because their repulsions are apparently offset by nuclear forces. matter appears to be electrically neutral means equal positive and negative therefore neutral charge.
Group VIIA Halogens
from words "sea" or "salt" greek.
Elements can be metals, nonmetals, or metalloids
allows to study way properties vary with an element's position in the table.some nonmetals have properties that lie between true metals and true nonmetals called metalloids. most are metals and slightly over a dozen nonmetals and only a handful are metalloids.
Group IIA
also metals. their oxygen compounds are alkaline too, but many of the compounds ar enable to dissolve in water. alkaline earth metals because of where they are in nature.
Relative atomic masses of elements can be found
atoms have a constant atomic mass(or atomic weight) relative mass is found with ratios for example FtoH atom ratio - 1 to 1 FtoH mass ratio - 19.0 to 1.00 How could a 1to1 atom ratio give to a 19.0to1.00 mass ratio? only if each fluorine is 19 times heavier than each H atom. we don't know actual mass of H and F, but how they compare.(relative masses)
hydrates
certain compounds form crystals that contain water molecules. water molecules can be driven off by heating the crystals.will absorb water again. compounds whose crystals contain water molecules in fixed ratios are called hydrates. the raised dot indicates that the water molecules are not bound too tightly in the crystal and can be removed. dehydration causes changes of color.
chemical equations describe what happens in a chemical reaction
chemical equation describes what happens when a chemical reaction occurs. FOR EX: 2H(2) = O(2) -> 2H(2)O the two substances to the left of the arrow are reactants. to the right, the product. numbers in front of the formulas are called coefficients. coefficients are needed for the law of conservation of mass. same types of element present before and after. BALANCED.
chemical formulas
chemical formulas - chemical symbols used to express atoms. free element - one that is not combined with another element in a compound.
more
chemists naturally work with whatever mixtures of isotope comes with a given element as it occurs naturally. we speak of the average atom of an element the on isotope with an atomic mass equal to its mass number is c12.
daltons atomic theory
concept atoms began nearly 2,500 years ago when certain Greek philosophers expressed the belief that matter is ultimately composed of tiny individual particles comes from Greek word atomos(not cut) philosophers conclusions were not supported by any evidence. remained a philosophical belief until law of conservation of mass and law of definite proportions
atoms are composed of subatomic particles
earliest theories about atoms imaged them to be indestructible and unable to be broken into smaller pieces. atoms are not as indestructible as dalton had thought. experiments performed showed that atoms are made of subatomic particles
metalloids have physical
electrical conductivity, metal, tend to be semiconductors, don't conduct s well as metals.behave as nonmetals
protons, neutrons, and electrons
experiments have shown that atoms are made of three types of subatomic particles PROTONS, NEUTRONS, ELECTRONS At the center of an atom, a nucleus, where protons and neutrons are found. protons and neutrons are called nucleons, electrons fill remaining atom volume protons carry a single unit of positive charge electrons carry a single unit of opposite charge, a negative charge
hydrogen forms compounds with many nonmetals
hybrides - compounds that elements form with hydrogen the number of spaces to the right that we hace to move in the periodic table to get a noble gas = number of hydrogen atoms.
...
hydrocarbons are the foundation of organic chemistry. derived from them are other compoundsal example are the alcohol compounds (alcohols) the atoms of OH replace a hydrogen in a hydrocarbon. CH(4) - remove one H and replace with OH ethanol - another familiar alcohol - comes from fermentation of grains
Law of definite proportions
in a given compound. the elements are always combined in the same proportion by mass. compound - chemically combined in a definite fixed proportion by mass. if we decompose the compound we always get the same ratio if we form water from oxygen and hydrogen ratio same. EX. 100g oxygen ______ (chemical reaction occurs consuming 8g and 1g hydrogen) 1 hydrogen g. = 9g water/92 g oxygen
metals have distinctive physical properties
malleable - rolled into thin sheets, ductile - drawn into wire hardness (cut with a knife?) solid at room temp(mercury)
Mendelev created the first periodic table
mendelev and german physicist julius lothar meyer. they independently made similar periodic tables. mendeleev published first he found that when he arranged in order of atomic mass, similar chemical properties were repeated over and over again. example, lithium, sodium, potassium, rubidium, and cesium are soft metals that are reactive towards water. they form compounds with chlorine with a 1 to 1 ratio of metal to chlorine. arranged by increasing atomic mass, groups and periods. similar properties in same groups.accurately predicted gaps as to where some elements found may be. tellurium and iodine gave him issues te had higher atomic mass, so he switched their order.
metal ad nonmetallic
metalloids appear between metals and nonmetals.
molecular form
molecular compounds are formed when nonmetallic elements combine. although very few nonmetals, the amount of molecular substances formed by them is huge. variety is a factor. most molecules are more complex.
molecular compounds
molecule - electronically neutral particle consisting of tow or more atoms applies to many elements and molecular compounds
diatomic molecules
molecules composed of two atoms each among them are gases.the formula for molecular hydrogen is H2(O2, N2)
nonmetals lack metal properties
most often compounds. many solids at room temp while many gases at room temp. lack malleability and ductility. broad range of chemical reactivity.
Law of conservation of mass
no detectable gain or loss of mass occurs in chemical reactions. matter is conserved. if a reaction occurs in a vessel where no matter can enter or leave, then it will be identical to the matter before.
Group VIIIA Noble Gases
noble gases. used to be called inert gases until it was discovered that heavier members of the group show a small degree of chemical reactivity. gold is a noble metal (so few can react with)
atomic numbers define elements and mass numbers describe isotopes
number of protons distinguish one element from another. thus atomic number(Z) = number of protons in the nuclei of any atoms. most elements exist in nature called isotopes that only differ in mass. isotopes of same elements differ with the number of neutrons (same protons different neutrons) Isotope mass number(A) = (number of protons) + number of neutrons X stands for the chemical symbol for the isotope.
compounds of carbon form the basis
organic compounds - combining with carbon elements organic chemistry - study of organic - from living organisms hydrocarbons - compounds of carbon and hydrogen simplest is CH4 methane. the first 6 are called the alkane series. as the molecules become bigger, their boiling points increasee. structural formulas indicate how they are combined. Ethane : C(2)H(6) ---> CH(3)CH(3) The alkanes are common substances. alkanes are not the only hydrocarbons. there are three two carbon hydrocarbons, ethylene, ethane, and acetylene
SPEICLA TERMINOLOGY ASSOCIATED WITH THE PERIODIC TABLE
placed below table for space reasons. because of similarities in each group, we call them families of elements. elements in longer columns (A groups) are known as representative elements or main group elements. those that are in B groups are transition elements. and each row is named by the element that it follows. elements 58-71 are lantahnifrd because lanthanum. lanthanides are also called RARE EARTH
formulas and equations
property almost every element has is the ability to combine with others.
cont 2.
proton and neutron more massive than electron. almost all atom mass in nucleus. almost all volume occupied by electrons.
average atomic masses can be calculated from isotopic abundances
relative atomic mass of elements were originally determined in a way similar to h and fl comparison. method have been developed to measure precisely
modern experimental evidence exists for atoms
scanning tunneling microscope invelted in 1980s tip brought to electrically conducting surface and an electric current bridging the gap is begun. flow of current is extremely sensitive to the distance between the tip of the probe and the sample. as the tip is moved across the surface, height adjusted ti keep the current flow constant
brownian motion
shows existence of molecules. tiny grains are jiggling when suspended in liquid. explanation, molecules. robert brown. chemical bonds hold together molecules atoms.chemical bonds arise from sharing of electrons between one atom to another. GROUP OF ATOMS THAT MAKE UP A MOLECULE MOVE ABOUT TOGETHER AND BEHAVE AS A SINGLEPARTICLE.\ Chemical formulas we use to describe compositions of molecules are called molecular formulas.
states
states specified with (s)(g)(l) if a solution is dissolved in water, we will write aq(aqueous solution)
daltons explains law of multiple proportions
suppose a molecule of sulfur trioxide contains one sulfur and three oxygen atoms, and a molecule of sulfur dioxide contains one sulfur and two atoms. we find they are in ratio 3 to 2. because all oxygen atoms has same mass ratio must be 3 to 2 also.
the atomic theory was proposed by John Dalton
the two laws were the experimental foundation for the atomic theory. ANSWERED QUESTION: What must be true about the nature of matter given the truth of these laws? beginning of 19th century, dalton used the greek concept to make sense of these laws. if atoms exist they must have certain properties to account for these laws. - list of properties - dalton's atomic theory
the modern periodic table arranges elements by atomic number
when atomic numbers were found, it was discovered that his table went by increasing atomic number. Te and i NO LONGER A PROBLEM.
compound formula
when more than one atom of an element is given by a SUBSCRIPT after the symbol.no sub = 1
the periodic table is used to organize and correlate facts
when we study different kinds of substances, we find that some are elements and others are compounds. among compounds, some are composed of discrete molecules.m others are made up of atoms that have acquired electrical charges. need for organization
Law of Multiple Proportions
whenever two elements form more than one compound the different masses of one elements that combine with the same mass of other element are in the ratio of small whole numbers.
