Physical Science Ch. 19

Section 1 Stability in Bonding

Compounds Two or more elements combining to make a substance Compounds have different properties than the elements that make them up

Chemical Formula Subscript composed of symbols and subscripts indicating the number of atoms of an element in a compound. Subscript Means “written below”

Atoms form compounds when the compound is more stable than the separate atoms. Noble gases Elements in far right column Are more chemically stable than other elements because they have a complete outer energy level.

Stable Compounds Chemical bond Elements that do not have full outer energy levels are more stable in compounds. Atoms can lose, gain, or share electrons to get a stable outer energy level. Chemical bond the force that holds atoms together in a compound.

Section 2 Types of Bonds

Forming a bond Chemical Bonds When two elements come together by either transferring or sharing electrons When elements lose or gain electrons The result of bonding is a net charge of zero

Ion A charged particle because it has more or fewer electrons than protons. Cation Positively charged ion When an atom loses an electron Anion Negatively charged ion When an atom gains an electron

Molecules Covalent bond Neutral particles formed as a result of sharing electrons. Covalent bond the force of attraction between atoms sharing electrons.

Ionic bond Chemical Bonding the force of attraction between opposite charges of the ions Chemical Bonding Result is a neutral compound. Sum of the charges is zero.

Atoms can form double or triple bonds depending on whether they share two or three pairs of electrons Saturated all single bonds Unsaturated Not all single bonds Must contain at least one double or triple bond

Polar molecule Nonpolar molecule Opposite ends have opposite charges electrons are shared equally.

Ionic Compounds Covalent Compounds With ions (cations and anions) Between metal and non-metal Transfer of electrons Covalent Compounds With molecules Between two non-metals Sharing of electrons

Writing Formulas and Naming Compounds Section 3 Writing Formulas and Naming Compounds

Chemists use symbols from the periodic table to write formulas for compounds. Binary compound composed of two elements Oxidation number how many electrons an atom has gained, lost, or shared to become stable The apparent charge on an element

When writing formulas, remember that the compound is neutral. To write formulas Use oxidation numbers Least common multiples When writing formulas, remember that the compound is neutral. A formula must have the correct number of positive and negative ions so the charges balance The formula must have a neutral charge

Writing Binary Compounds Write down first element & it’s oxidation number Write down second element & it’s oxidation number Add multiples of the appropriate element until total charge is zero Use subscripts to show ratio of the atoms of each element

Calcium Oxide Ca +2 O-2 +2 -2 So 1 Ca and 1 O CaO

Lithium Nitride Li +1 N-3 +1 -3 +1 So 3 Li and 1 N Li3N

Magnesium Phosphide Mg +2 P-3 +2 -3 +2 -3 So 3 Mg and 2 P Mg3P2

Potassium Sulfide K +1 S-2 +1 -2 +1 So 2 K and 1 S K2S

Naming Binary Compounds Write down name of first element Write down name of second element Change the ending of the second element to –ide

NaCl Sodium Chlorine -ide Sodium Chloride

K2O Potassium Oxygen -ide Potassium Oxide

Poly Polyatomic ion Means “many” positively or negatively charged, covalently bonded group of atoms Many atoms

Binary covalent compounds Hydrate compound with water chemically attached to it Binary covalent compounds Name by using prefixes to indicate how many atoms of each element are in the compound

Prefixes for Covalent Compounds Mono- Di- Tri- Tetra- Penta- Hexa- Hepta- Octa- Non- Dec- Prefixes for Covalent Compounds