 loss of valence electrons

 gain of negatively charged electrons  name of the anion typically ends in -ide

 Anion that gains 2 electrons

 compounds composed of cations and anions  electrically neutral  Held together by IONIC BOND › electrostatic forces

 Chemical Formula › indicates the number of atoms of each element found in each molecule of that compound  Formula Unit = lowest whole-number ratio of ions in an ionic compound › Ionic compounds do not exist as individual molecules

 All the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable). CaP Lets do an example by combining calcium and phosphorus:

CaP

Ca 2+ P

Ionic Bonding Ca 2+ P Ca

Ionic Bonding Ca 2+ P 3- Ca

Ionic Bonding Ca 2+ P 3- Ca P

Ionic Bonding Ca 2+ P 3- Ca 2+ P

Ionic Bonding Ca 2+ P 3- Ca 2+ P Ca

Ionic Bonding Ca 2+ P 3- Ca 2+ P Ca

Ionic Bonding Ca 2+ P 3- Ca 2+ P 3- Ca 2+

Ionic Bonding = Ca 3 P 2 Formula Unit the smallest representative particle

 crystalline solids at room temperature  arranged in repeating three-dimensional patterns  very stable structure  high melting points

 Ionic compounds conduct electric current when melted or dissolved in water

 a neutral group of atoms joined together by covalent bonds  there is no such thing as a molecule of sodium chloride or magnesium chloride  ionic compounds exist as collections of positively and negatively charged ions

 Molecular compounds have relatively lower melting and boiling points than ionic compounds › gases or liquids at room temperature

 shows how many atoms of each element a molecule contains › water molecule = two hydrogen atoms and one oxygen atom  molecular formula = H 2 O. › carbon dioxide molecule = two oxygen atoms and one carbon atom  molecular formula = CO 2  Note: › If there is only one atom, the subscript 1 is omitted

 The molecular formula for ethane is C 2 H 6 › one molecule of ethane contains two carbon atoms and six hydrogen atoms  reflects the actual number of atoms in each molecule › not necessarily lowest whole-number ratios

 electron sharing occurs so that atoms attain the electron configurations of noble gases  likely to form covalent bonds: › atoms of the nonmetals and metalloids › Groups 4A, 5A, 6A, and 7A

 Two atoms held together by sharing a pair of electrons

pair of valence electrons not shared between atoms is called an unshared pair

 two shared pairs of electrons = double covalent bond  sharing three pairs of electrons = triple covalent bond.

 tightly bound group of atoms that has a positive or negative charge and behaves as a unit

 The negative charge of a polyatomic ion shows the number of electrons in addition to the valence electrons of the atoms present