Compounds Chapter 3.1 A molecule is a group of atoms in which the atoms are bond together by 1 or more pairs of electrons.

If H 2 0 is water what is H ?  Drinking……  Water is a compound with elements chemically bonded in a formula, H 2 O  H is for hydrogen;  O is for oxygen;  2 means there are two ions of hydrogen  there is only one ion of oxygen  Note: do not write a one for the oxygen in the formula

MgO C 6 H 12 O 6 2 SO 2 Mg(OH) 2 3Sn(Cr 2 O 7 )

 Remember that atoms “WANT” to have full outer shells unpairedvalence electrons interact and t  When two atoms get close together, their unpaired valence electrons interact and t here are two ways they can get that: 1. They can steal (lose/gain) electrons 2. They can share electrons with other atoms

positive and negative ions  Made up of positive and negative ions.  Metal + Non-Metal  Electrons are given and taken

‘full’ outer shell of valence electrons  So each atom in the compound attempts to have a ‘full’ outer shell of valence electrons.  Unpaired electrons are involved in the bonding and the lone pair electrons are not.

 Sodium (Na) & Chlorine (Cl)  metals lose electrons and non-metals gain electrons  Ionic Compounds form when electrons are transferred from positive (+) ions to negative (-) ions.

12 p 12 n +2 Magnesium Sulfide - MgS 16 p 16 n 2- The number of bonds an atom wants to form is determined by the number of e - in the outer shell that an element wants to donate or borrow. - In other words its combining capacity (ion charge) Example: Ca = +2 therefore donates 2 electrons Cl = -1 therefore borrows 1 electron

 lithium and oxygen form an ionic bond in the compound  Li 2 O lithium oxygen + Electrons are transferred from the positive ions to negative ions Li thium oxide, Li 2 O

Ionic Lattice  We think of (and write) ionic compounds in lowest terms, but in reality they are found as a network – called an “ionic lattice”

Covalent Compounds  made up of negative ions  Non-metal + Non-metal  Share electrons Negative charge

9 p 10 n Fluorine Gas – F 2 9 p 10 n 9 p 10 n

POLYATOMIC ION A group of atoms that tend to stay together and act as one charged ion

Some Compounds with Polyatomic Ions

More Compounds with Polyatomic Ions Table 5.7