Covalent Bonding electrons are shared Terms Valence electrons

Covalent Bonding …electrons are shared

Terms • Valence electrons - in the outer shell/orbital • Nonmetals – on the right side of the p. t. • Noble gases – group 18, have 8 valence e. Valence electrons 3 4 5 6 7 8 Nonmetals

Covalent bonds • Nonmetals hold onto their valence electrons. • They can’t give away electrons to bond. • Still want noble gas configuration. • Get it by sharing valence electrons with each other. • By sharing both atoms get to count the electrons toward noble gas configuration.

Covalent Bonding • In a covalent bond the electrons are the “glue” that holds the atoms together. • Only nonmetals and Hydrogen. • Different from an ionic bond because they actually form molecules. G. N. Lewis

Covalent Bonding: Hydrogen H • + H • H : H • The two electrons are shared evenly between the two hydrogen atoms. • It is as if each atom has two electrons – the noble gas configuration of [He]. H : H

Lewis Structures • A Lewis structure is a way of drawing a molecule that shows all valence electrons as dots or lines that represent valence electrons. eg. The Lewis structure for H 2 can be drawn in two ways: H: H or H–H A single line represents two covalently shared electrons – also known as a single bond.

Lewis Structures • The Lewis Structure for F 2: • Two electrons are shared between the two F atoms (one single covalent bond). • Each F atom also has three unshared electron pairs. These non-bonding electron pairs are called lone pairs.

Single Covalent Bond • A sharing of two valence electrons. • Two specific atoms are joined.

The Octet Rule • Note that by sharing electrons, it is as if each F atom has eight electrons - the noble gas configuration. • The Octet Rule: Main group elements with more than two valence electrons gain, lose, or share electrons to achieve a noble gas configuration characterized by eight valence electrons.

Covalent bonding • Fluorine has seven valence electrons • A second atom also has seven By sharing electrons …both end with full orbitals 8 Valence electrons F F 8 Valence electrons

How to show they formed • It’s like a jigsaw puzzle. • You have to know what the final formula is. • You put the pieces together to end up with the right formula. • For example- show water is formed with covalent bonds.

Water H 2 O H Each hydrogen has 1 valence electron Each hydrogen wants 1 more O The oxygen has 6 valence electrons The oxygen wants 2 more They share to make each other happy

Water H 2 O • Put the pieces together • The first hydrogen is happy • The oxygen still wants one more H O

Water • The second hydrogen attaches • Every atom has full energy levels • A pair of electrons is a single bond HO H

Multiple Bonds • Sometimes atoms share more than one pair of valence electrons. • A double bond is when atoms share two pair (4) of electrons. • A triple bond is when atoms share three pair (6) of electrons.

Carbon dioxide CO 2 • Carbon is central atom C O – Carbon has 4 valence electrons – Wants 4 more • Oxygen has 6 valence electrons – Wants 2 more

Carbon dioxide • Attaching 1 oxygen leaves the oxygen 1 short and the carbon 3 short CO

Carbon dioxide l Attaching the second oxygen leaves both oxygen 1 short and the carbon 2 short OC O

Carbon dioxide The only solution is to share more l Requires two double bonds l Each atom gets to count all the atoms in the bond l 8 valence electrons O CO

Lewis Structures

How to draw them • Add up all the valence electrons. • Count up the total number of electrons needed to make all atoms have 8. • Subtract. • Divide by 2 • This tells you how many bonds to draw. • Fill in the rest of the valence electrons to fill atoms up.

Tips for Lewis Structures • Group 14 almost always goes in the center • Hydrogen and halogens always go on the outside. • Hydrogen and halogens only form 1 bond • Group 15 always has 1 lone pair • Group 16 always has 2 lone pairs • Group 17 (halogens) always has 3 lone pairs

Examples N H • NH 3 – N - has 5 valence electrons wants 8 • H - has 1 valence electrons wants 2 • NH 3 has 5+(3*1) = 8 • NH 3 wants 8+(3*2) = 14 – (14 -8)/2= 3 bonds • 4 atoms with 3 bonds

Examples • Draw in the bonds • All 8 electrons are accounted for • Everything is full H H NH

Examples HCN • C is central atom – C - has 4 valence electrons wants 8 – N - has 5 valence electrons wants 8 – H - has 1 valence electrons wants 2 • HCN has 1+4+5 = 10 • HCN wants 2+8+8 = 18 – (18 -10)/2= 4 bonds • 3 atoms with 4 bonds -will require multiple bonds (not to H)