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Chapter 2

Atoms and Elements

Atom The smallest identifiable unit of an element
Law of Conservation of Mass In a chemical reaction, matter is neither created not destroyed
Law of Definite Proportions All samples of a given compound, regardless of their source or how they were prepared, have the same proportions of their constituent elements
Law of Multiple Proportions When two elements(call them A and B) form two different compounds, the masses of element B that combine with 1g of the element A can be expressed as a ratio of small whole numbers
1. Atomic Theory 1. Each element is composed of tiny, indestructible particles called atoms.. 2. All atoms of a given element have the same mass and other properties that distinguish them from the atoms of other elements..
2. Atomic Theory 3. Atoms combine in simple, whole-number ratios to form compounds.. 4. Atoms of one element cannot change into atoms of another element. In a chemical reaction, atoms only change the way that they are bound together with other atoms
Electron A negatively charged, low mass particle present within all atoms
Mass of Electron 9.10x10^-28g
Radioactivity The emission of small energetic particles from the core of certain unstable atoms
1. Nuclear Theory 1. Most of the atoms's mass and all of its positive charge are contained in a small core called the nucleus.. 2. Most of the volume of that atom is empty space, throughout which tiny, negatively charged electrons are dispersed..
2. Nuclear Theory 3. There are as many negatively charged electrons outside the nucleus as there are positively changed particles(named protons) within the nucleus, so the atom is electrically neutral
Neutrons Neutral particles within the nucleus
Atomic Mass Unit(amu) Defined as 1/12 the mass of a carbon atom containing six protons and six neutrons
How are Elements Defined An Element is defined by the number of protons it contains
Atomic Number(Z) The number of protons in an atom's nucleus
Chemical Symbol A one or two letter abbreviation listed directly below its atomic number on the periodic table
Isotopes Atoms with the same number of protons but different numbers of neutrons. "Same element, different mass"
Natural Abundance of Isotopes The percentage of the amount of a type of element found in a sample of those atoms
Mass Number(A) The sum of the number of neutrons and protons in an atom. A = number of protons(p) + number of neutrons(n)
Ions Atoms that gain or lose electrons. Charged atoms
Cation Positively charged ions. e^-1's < # P's Ex: Li+
Anion Negatively charged ions. e^-1's > # P's Ex: F-
Periodic Law When the elements are arranged in order of increasing mass, certain sets of properties recur periodically
Metals Metals lie on the lower left side and middle of the periodic table and share common properties: they are good conductors of heat and electricity, malleable, can be drawn into wires(ductility), shiny, tend to lose electrons when undergo chemical changes.
Nonmetals Lie on the upper right side of periodic table. Share varied properties: some are solids at room temperature, other are liquid or gases, all poor conductors of heat and electricity, all tend to gain electrons when undergo chemical changes
Metalloids Exhibit mixed properties: several classified as semiconductors because of their intermediate(and highly temperature - dependent) electrical conductivity
Main Group Elements Properties tend to be largely predictable based on their position in the periodic table. Labeled with a number and letter A
Transition Elements Properties tend to be less predictable based simply on their position in the periodic table. Labeled with number and letter B
Family(group) Elements Each column within the main-group regions of the periodic table
Noble Gases Elements under group 8A. These are mostly unreactive
Alkali Metals Group 1A elements. All reactive metals
Alkaline Earth Metals Group 2A elements. Also all fairly reactive, although not quite as reactive as the alkali metals.
Halogens Group 7A elements. Very reactive nonmetals.
Ions and the Periodic Table A main-group metal tends to lose electrons, forming a cation with the same number of electrons as the nearest noble gas.. A main-group nonmetal tends to gain electrons, forming and anion with the same number of electron as the nearest noble gas
Atomic Mass The average mass for each element
Calculating Atomic Mass Atomic Mass of Element = (fraction of isotope 1 x mass of isotope 1) + (fraction of isotope 2 x mass of isotope 2) + (fraction of isotope 3 x mass of isotope 3) + ......
Mass Spectrometry A technique that separates particles according to their mass
Mole(mol) A mole is the amount of material containing 6.02214 x 10^23 particles. Called the chemist's "dozen". This number is called Avagadro's Number 1 mol = 6.02214 x 10^23 particles. This number is often rounded to *6.022 x 10^23*.
Mole Specific Value The value of the mole is equal to the number of atoms in exactly 12 grams of pure carbon-12(12gC = 1 mol C atoms = 6.022x10^23 C atoms)
Molar Mass The mass of 1 mol of atoms of an element. An element's molar mass in grams per mole is numerically equal to the element's atomic mass in atomic mass units. 1 amu = 1g/mol
Subatomic Particles Three kinds... 1. Proton.. 2. Neutron.. 3. Electron
Proton(a.k.a. Atomic Number) The number of protons is unique to each element.. Mass(AMU) = 1.00727 Relative Charge = +1
Neutron Mass(AMU) = 1.00866 Relative Charge = 0
Electron Don't affect mass.. Mass(AMU) = 0.00055 Relative Charge = -1
Charge of Zinc Ion +2
Charge of Silver Ion +1
Created by: TimChemistry1



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