Chapter 2: Atoms and Elements

H

Hydrogen

He

Helium

Li

Lithium

Be

Beryllium

B

Boron, metalloid

C

Carbon

N

Nitrogen

O

Oxygen

F

Fluorine

Ne

Neon

Na

Sodium

Mg

Magnesium

Al

Aluminum

Si

Silicon, metalloid

P

Phosphorus

S

Sulfur

Cl

Chlorine

Ar

Argon

K

Potassium

Ca

Calcium

Sc

Scandium

Ti

Titanium

V

Vanadium

Cr

Chromium

Mn

Manganese

Fe

Iron

Co

Cobalt

Ni

Nickel

Cu

Copper

Zn

Zinc

Ga

Gallium

Ge

Germanium, metalloid

As

Arsenic, metalloid

Se

Selenium

Br

Bromine

Kr

Krypton

Rb

Rubidium

Sr

Strontium

Cs

Cesium

Ba

Barium

Mo

Molybdenum

Ag

Silver

Sn

Tin

Sb

Antimony, metalloid

Te

Tellurium, metalloid

Xe

Xenon

Rn

Radon

At

Astatine, metalloid

W

Tungsten

Pd

Palladium

Pt

Platinum

Au

Gold

Hg

Mercury

Pb

Lead

Bi

Bismuth

Po

Polonium

Cm

Curium

U

Uranium

Law of Conservation of Mass

In a chemical reaction, matter is neither created nor destroyed.

Law of Definite Proportions

Also called the Law of Constant Composition. It says that 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 1 g of element A can be expressed as a ratio of small whole numbers.

John Dalton's Atomic Theory (4 Points)

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.
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.

Cathode Rays

A stream of electrons produced when a high electrical voltage is applied between two electrodes within a partially evacuated tube.

J.J. Thomson

used the cathode ray tube to discover electrons

electron

a negatively charged, low mass particle present within all atoms

Robert Millikan

Performed the "oil-drop" experiment in which he deduced the charge of a single electron

Plum-pudding Model

J.J. Thomson's model of an atom, in which he thought electrons were randomly distributed within a positively charged sphere.

Radioactivity

the emission of small energetic particles from the core of certain unstable atoms; discovered by Becquerel and Curie

Three types of radioactivity

1. alpha particles
2. beta particles
3. gamma rays

Alpha particles are positively charged and they are by far the most massive of the three.

Rutherford's Gold Foil Experiment

Alpha-particles were directed at a thin sheet of gold foil; most passed through the foil, but a few were deflected. This disproved Thomson's Plum-pudding model and led to the discovery of a small, dense, positively charged nucleus.

Rutherford's Nuclear Theory (3 Parts)

1. Most of the atom's mass and all of its positive charge are contained in a small core called the nucleus.
2. Most of the volume of the atom is empty space, throughout which tiny, negatively charged electrons are dispersed.
3. There are as many negatively charged electrons outside the nucleus as there are positively charged protons within the nucleus, so the atom is electrically neutral.

proton

A subatomic particle that has a positive charge and that is found in the nucleus of an atom

neutron

A subatomic particle that has no charge and that is found in the nucleus of an atom. The mass of a neutron is similar to that of a proton.

atomic mass unit (amu)

Defined as 1/12 the mass of a carbon-12 atom, which contains 6 protons and 6 neutrons.

atomic number (Z)

the number of protons in the nucleus of an atom

Chemical symbol

A unique one- or two-letter abbreviation listed directly below its atomic number on the periodic table. The first letter is always capitalized. The second letter is never capitalized.

isotope

Atoms with the same number of protons, but different number of neutrons.

natural abundance of isotopes

the relative amount of each different isotope in a naturally occurring sample of a given element

mass number (A)

the sum of the number of neutrons and protons in an atomic nucleus

Isotope notation 1

The representation of a specific isotope. The atomic number is listed below the symbol, the mass number above.

Isotope notation 2

the chemical symbol or chemical name followed by a dash and the mass number of the isotope

ions

positively and negatively charged atoms

Mendeleev's Periodic Law

When 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 some common properties: they are good conductors of heat and electricity, they can be pounded into flat sheets (malleability), they can be drawn into wires (ductility), they are shiny, they lose electrons

ductility

The ability to be pulled into thin wires

malleability

the ability of a substance to be hammered or beaten into thin sheets

nonmetals

Nonmetals lie on the upper right side of the periodic table. They are poor conductors of heat and electricity, and they gain electrons when they undergo chemical changes.

metalloids

elements that lie along the zigzag diagonal line that divides metals and nonmetals. They exhibit mixed properties. Examples of metalloids include B, Si, Ge, As, Sb, Te, At

semiconductors

Several metalloids are classified as semiconductors, because of their intermediate (and temperature dependent) electrical conductivity.

main-group elements

elements whose properties tend to be largely predictable based on their position in the periodic table

transition elements

elements whose properties tend to be less predictable based simply on their position in the periodic table.

Family or Group of elements

is a vertical column in the periodic table of the chemical elements.

Period of elements

A horizontal row of elements in the periodic table

Noble Gases

Group 8A or 18 - Unreactive or inert gases.

Alkali Metals

Group 1A - All reactive metals.

Alkaline Earth Metals

Group 2A - Fairly reactive metals, although not as reactive as alkali metals.

Halogens

Group 7A or 17 - Very reactive nonmetals.

Cation

A positively charged ion that forms when a metal loses electrons.

Anion

A negatively charged ion that forms when a nonmetal gains electrons.

Atomic Mass

The average mass of all the isotopes of an element.