Lecture 2 - Bonds

Question 1

Location and Information on electrons

Answer 1

electrons are in energy levels around the nucleus called the electron cloud.
The higher the energy level, the more energy is required for the electron to occupy that part of the cloud.
The outermost part of the electron cloud is called the valence shell.
The max number of valence electrons is 8.

Question 2

When is an atom most stable?

Answer 2

When it has 8 valence electrons.

Question 3

What is an octet?

Answer 3

An atom that has 8 valence electrons which is gained through the loss of, gain of and sharing of electrons.

Question 4

What is the octet rule?

Answer 4

Atoms that form bonds with other atoms by sharing electrons or transferring electrons is known as the octet rule.

Question 5

What are the chemical bonds called?

Answer 5

Covalent
Ionic
Hydrogen
Metallic

Question 6

What is the difference in Hydrogens and Heliums valance electrons?

Answer 6

Hydrogen requires only 1 more electron to fill its valence electrons (total 2 valence electrons).
Helium has 2 valence electrons (full) and is stable so it does not bond with other atoms.

Question 7

What are ionic bonds?

Answer 7

Formed by the attraction of 2 oppositely charged atoms. They form when atoms gain or lose electrons. If the compound has a metal, then it is an ionic bond. Typically between non-metal and metal.

The non-metal gains the electrons where as the metal loses the electrons. Metals that lose electrons are called positive cations, & non-metals that gain electrons are called negative anions.

Question 8

What is a covalent bond?

Answer 8

The sharing of electrons. If atoms have a covalent bond and they are the same atom type, these are called diatomic molecules eg. Cl-Cl. Typically between non-metal and non-metal.

Question 9

What is electronegativity?

Answer 9

The power of an atom to attract electron density in a covalent bond. Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons

Question 10

What is Pauling’s electronegativity scale?

Answer 10

Displays the electronegativity of elements. The higher the value, the higher the electronegative the element is. The most electronegative element is Fluorine with a value of 4.0.

Question 11

What is an ion?

Answer 11

Any atom with more or less electrons than it is supposed to have.

Question 12

What is a polyatomic ion?

Answer 12

A group of atoms that act like 1 ion.

Question 13

What are the properties of ionic compounds?

Answer 13

Crystalline Structure - a regular repeating arrangement of ions in the solid. Positive cations stick to the negative anions like a magnet.
Ions are strongly bonded - rigid structure
High melting points - Because of the strong forces between the ions.

Question 14

Do ionic compounds conduct?

Answer 14

Conducting electricity means allowing charges to move. In a solid the ions are locked in place meaning that they are insulators. When melted, the ions can move around so the ionic compound is then a conductor, however to melt the ionic compound, 800 degrees C is required. Dissolved in water, they conduct.

Question 15

What is a single covalent bond?

Answer 15

The sharing of 2 valence electrons between non-metals and hydrogen only, These differ from ionic bond because these actually form a molecule. 2 specific atoms are joined. e.g H20 has 2 single covalent bonds.

Question 16

What are multiple bonds?

Answer 16

When atoms share 2 pairs of electrons (double bond - 4 electrons shared) e.g CO2 = Carbon and Oxygen share 2 electrons each with each other.
or when they share 3 pairs of electrons (triple bond - 6 electrons shared)

Question 17

How do you draw and calculate the number of bonds?

Answer 17

Calculate the number of valence electrons of the compound and subtract it what is left to achieve the desired valence electrons. Divide by 2.

Question 18

How are bonds indicated?

Answer 18

A line represents a bond and each line is 2 valence electrons.

Question 19

What is a coordinate covalent bond?

Answer 19

When an atom donates both electrons in a covalent bond e.g CO (Carbon Monoxide)

Question 20

What is a non-polar and polar bond?

Answer 20

A non-polar bond is when 2 same atoms share electrons equally. A polar band is when 2 different atom types share bond unequally.

Question 21

What are the electronegative values for non-polar, polar and ionic bonds.

Answer 21

Covalent non-polar = 0.0 - 0.3
Covalent polar = 0.3 - 1.67
Ionic = >1.67

Question 22

What are intermolecular Forces?

Answer 22

These are the attractions between molecules and are not nearly as strong as the INTRAmolecular attractions that hold compounds together. However, they are strong enough to control physical properties such as boiling & melting points, vapour pressure and viscosities.
These forces are grouped and referred to as Van Der Waals Forces.

Question 23

What is a dipole-dipole interaction?

Answer 23

Molecules that have permanent dipoles are attracted to each other. The positive end of one is attracted to the negative end of the other and vice versa. These forces are only important when the molecules are close to one another.

Question 24

What is hydrogen bonding?

Answer 24

The dipole-dipole interactions experienced when hydrogen is bonded to N, O or F are unusually strong and these interactions are called hydrogen bonds. This is due to the high electronegativity of these elements. Also when hydrogen bonds with any of these elements, the hydrogen nucleus is exposed. This is the strongest of the intermolecular forces.

Question 25

What is an example of a covalent network solid win which atoms are covalently bonded to each other?

Answer 25

Diamond - Hard and has a high melting point

Question 26

What is an example of a molecular solid in which atoms are held together with van der Waals forces.

Answer 26

Graphite - Softer and has a lower melting point

Question 27

What does partially positive ad partially negative changes mean in electronegativity?

Answer 27

Electrons are more inclined towards an atom in a compound rather than the other (inclined to = partially negative) (away from = partially positive). These opposite charges are called dipoles and will attract to one another of different molecules.