Chemistry Exam - Unit 1 and 2

Element

Element

a substance that cannot be broken down by any chemical reaction

Molecule

made up one or more atoms joined by covalent bond

Compound

substance made up of two or more different chemical elements combined in a fixed ratio

Atomic Number

number of protons in a nucleus

Mass Number

number of protons and neutrons added together

Atomic Mass

average mass of protons, neutrons and electrons in an atom, denoted by the symbol ‘u’

Group

vertical columns in the periodic table

Family

group of elements that have certain similar properties

Period

horizontal rows in the periodic table

Halogens or Noble Gases

“salt former” elements that form salts when they react to metal

Inert Gas

a gas that is non-reactive with other substances

Atomic Radius

measurement of the size of an atom in picometers

A.R. DECREASES ACROSS a period

• the more e- present in the outer energy level, the greater the attraction between the outer energy level and the nucleus

A.R. INCREASES DOWN in a group

• each new period means another energy level, which means a larger atom

Electronegativity

a measure of an atom’s ability to attract a shared pair of electrons WITHIN a covalent bond

EN INCREASES UP a group

EN INCREASES ACROSS the periodic table

• Fluorine - HIGHEST electronegativity (4.0)

• Francium - LOWEST electronegativity (0.7)

Ionization Energy

amount of energy required to remove an electron from an atom or ion

I.E. of metals is LOWER than I.E. of non-metals

I.E. INCREASES UP a group (due to an increase in atomic size)

I.E. INCREASES ACROSS in a period (due to a decrease in atomic size)

Electron Affinity

a measure of the change in energy that occurs when an electron is added to the outer energy level of an atom to form a negative ion

METALS have low E.A. compared to NON-METALS

E.A. INCREASE UP a group

E.A. INCREASES ACROSS a period

Ionic Bond

ions are held together by strong electrostatic forces

delta EN 1.7-3.3

Polar Covalent Bond

electrons shared unequally

delta EN 0.5-1.7

Non-polar Covalent Bond

equal sharing of electrons

delta EN 0-0.4

Examples of polar molecules

water, ammonia, sulfur dioxide

Examples of non-polar molecules

O2, CO2, methane, helium, gasoline

Intramolecular Bond

forces that hold atoms together within a molecule

• covalent and ionic bonds

Difference between Ionic Bond and Covalent Bond

ionic bond has a metal and non-metal and covalent has non-metal only

Intermolecular forces

forces that hold atoms together between a molecule

Hydrogen Bond

special type of dipole-dipole bonding that occurs when hydrogen bonds to N, O, or F

• strongest force

Dipole-Dipole Forces

forms between partial positive of one polar molecule and partial negative end of another

• stronger than LDF

LDF

one side of a molecule is slightly + charged and one side of another - charged

• weakest force

Four main classes of chemical reactions

Synthesis, Decomposition, Combustion, SD, DD

Isotope

atoms with the same number of protons but different number of neutrons

Radioisotopes

unstable chemical element that releases radiation as it becomes more stable

Alpha Particles

A positively charges particle with the same structure as the nucleus of a helium atom

Cannot pass through paper

Beta Particles

negatively charged particle identical to an electron

Passes through paper but not through aluminum

Gamma Rays

A form of high-energy electromagnetic radiation.

No mass, travels at the speed of light, PENETRATES most substances, but blocked by lead

Single Displacement

single displacements involving halogens and metals, look over the activity series

• metal displaces metal in a compound that is below it in the activity series

Incomplete Combustion

occurs when there is insufficient oxygen present

fuel + oxygen = CO2 + water + CO + C

Complete Combustion

reaction of a compound or element with 02 to form carbon dioxide and water

fuel + oxygen = CO2 + water

Covalent Bond

bond that forms as a result of sharing electrons