Lewis Structure (2)

What is a Lewis formula?

A Lewis formula is a diagram showing all valence electrons in a covalently bonded species.

What is another name for a Lewis formula?

A Lewis formula is also called a Lewis structure or electron dot diagram.

What does a Lewis formula show?

It shows bonding pairs and lone pairs of valence electrons.

What is a bonding pair?

A bonding pair is a pair of electrons shared between two atoms in a covalent bond.

What is a lone pair?

A lone pair is a pair of valence electrons not used in bonding.

How can electron pairs be shown in Lewis formulas?

Electron pairs can be shown as dots, crosses, a mixture of dots and crosses, or a line.

Why is Cl-Cl alone not a full Lewis formula?

Because it does not show all the electron pairs.

What is the first step in drawing a Lewis formula?

Count the total number of valence electrons for all atoms in the species.

What is the second step in drawing a Lewis formula?

Draw the skeletal arrangement to show how the atoms are connected.

Which atom is usually placed in the centre of a Lewis structure?

The central atom is usually the least electronegative atom.

What is the next step after drawing the skeleton?

Add bonding pairs between bonded atoms.

What do you do after adding bonding pairs?

Add lone pairs to complete octets, or duets for hydrogen, starting with the outer atoms.

What is the final check for a Lewis formula?

Check that all valence electrons have been used and that atoms have full octets or duets where appropriate.

How many electrons does hydrogen aim to have in its outer shell?

Hydrogen aims to have 2 electrons in its outer shell.

What is the octet rule?

The octet rule is the tendency of atoms to achieve 8 electrons in their outer shell.

How many valence electrons does carbon have?

Carbon has 4 valence electrons.

How many valence electrons does hydrogen have?

Hydrogen has 1 valence electron.

How many valence electrons does oxygen have?

Oxygen has 6 valence electrons.

How many valence electrons does nitrogen have?

Nitrogen has 5 valence electrons.

How many valence electrons does chlorine have?

Chlorine has 7 valence electrons.

How many total valence electrons are in CH4?

CH4 has 8 valence electrons in total.

How many lone pairs are on the central atom in CH4?

There are no lone pairs on the central carbon atom in CH4.

How many total valence electrons are in NH3?

NH3 has 8 valence electrons in total.

How many lone pairs are on nitrogen in NH3?

Nitrogen has 1 lone pair in NH3.

How many total valence electrons are in CCl4?

CCl4 has 32 valence electrons in total.

How many lone pairs does each chlorine atom have in CCl4?

Each chlorine atom has 3 lone pairs in CCl4.

How many total valence electrons are in H2O?

H2O has 8 valence electrons in total.

How many lone pairs are on oxygen in H2O?

Oxygen has 2 lone pairs in H2O.

How many total valence electrons are in CO2?

CO2 has 16 valence electrons in total.

What type of bonds are present in CO2?

CO2 contains two double bonds.

How many lone pairs does each oxygen have in CO2?

Each oxygen has 2 lone pairs in CO2.

How many total valence electrons are in HCN?

HCN has 10 valence electrons in total.

What type of bonds are present in HCN?

HCN has a single bond between H and C and a triple bond between C and N.

How many lone pairs are on nitrogen in HCN?

Nitrogen has 1 lone pair in HCN.

Do all molecules follow the octet rule?

No, some stable molecules do not follow the octet rule.

What does electron-deficient mean?

Electron-deficient means the central atom has fewer than 8 electrons around it.

Which elements commonly form stable compounds with incomplete octets?

Beryllium, boron, and aluminium commonly form stable compounds with incomplete octets.

Why is BeCl2 an exception to the octet rule?

Because beryllium has only 4 electrons around it in BeCl2.

Why is BF3 an exception to the octet rule?

Because boron has only 6 electrons around it in BF3.

How many lone pairs does each chlorine have in BeCl2?

Each chlorine has 3 lone pairs in BeCl2.

How many lone pairs does each fluorine have in BF3?

Each fluorine has 3 lone pairs in BF3.