PERIODIC TRENDS AND INTRAMOLECULAR FORCES

Question 1

Describe atomic mass

Answer 1

The mass of an atom of a chemical element expressed in atomic mass units. It is approximately equivalent to the number of protons and neutrons in the atom (the mass number) or to the average number allowing for the relative abundances of different isotopes

Question 2

Describe mass number

Answer 2

The mass of protons and neutrons in a specific isotope of an element

Question 3

Describe atomic number

Answer 3

Atomic number, the number of a chemical element in the periodic system, whereby the elements are arranged in order of increasing number of protons in the nucleus

Question 4

Describe atomic weight

Answer 4

the average mass of an atom of an element as it occurs in nature that is expressed in atomic mass units.

Atomic weight =
(% abundance isotope 1/100) x (mass of isotope 1) +
(% abundance isotope 2/100) x (mass of isotope 2) + …

Question 5

Define an isotope and how isotopes of the same element differ

Answer 5

An isotope is an atom with the same atomic number (number of protons) but different mass number, therefore a different number of neutrons. The notable difference of isotopes is their radioactivity. Often 1 isotope occurs more commonly, it is the most stable

Question 6

Understand the purpose and structure of the periodic table

Answer 6

The chemical elements are arranged in order of increasing atomic number. The horizontal rows are called periods and the vertical columns are called groups. Elements in the same group have similar chemical properties.

Question 7

In terms of periodic trends describe: metallic and non-metallic nature of the elements

Answer 7

Metallic character decreases diagonally right to left and increases diagonally left to right.

Question 8

In terms of periodic trends describe: atomic radius

Answer 8

Atomic radius of an element decreases down a group and backwards along a period

1/2 the diameter of a neutral atom

Atomic size increases with the number of shells

the size of an atom is determined by the distribution of electrons around its nucleus. The closer the electrons are to the nucleus, the more tightly they are bound, thus increasing the electronegativity of the atom

Question 9

In terms of periodic trends describe: effective nuclear charge

Answer 9

Zeff = Z (no. of protons) - S (number of shielding electrons)

The more shielding, the weaker the nucleus’ hold on the valence electrons, the greater the reactivity

Increases up a group and left to right across a period

Question 10

In terms of periodic trends describe: number of valence electrons

Answer 10

Valence electrons increase left to right across a period

Question 11

In terms of periodic trends describe: Ionisation energy

Answer 11

A measure of how difficult it is to remove the most loosely held electron from an atom in the gaseous phase

Largely based on Zeff

Ionisation energy increases left to right across a period and up a group

Question 12

In terms of periodic trends describe: Ionic radius

Answer 12

Atomic is the distance away from the nucleus. Atomic radius increases going from top to bottom and decreases going across the periodic table. Ionic radius is the distance away from the central atom.

Question 13

In terms of periodic trends describe: reactivity

Answer 13

The more shielding, the weaker the nucleus’ hold on the valence electrons, the greater the reactivity

Question 14

In terms of periodic trends describe: reactivity

Answer 14

Reactivity decreases as you go from left to right across a period. The farther to the left and down the periodic chart you go, the easier it is for electrons to be given or taken away, resulting in higher reactivity

The more shielding, the weaker the nucleus’ hold on the valence electrons, the greater the reactivity

Question 15

Describe the octet rule

Answer 15

The octet rule states that atoms tend to form compounds in ways that give them eight valence electrons and thus the electron configuration of a noble gas. One way is by sharing their valence electrons with other atoms (covalent bonding), the second way is by transferring valence electrons from one atom to another (ionic bonding).

Question 16

Describe:

1. An anion and how they are formed
2. A cation and how they are formed

Answer 16

1. An anion is an ion with a negative charge, formed by an atom gaining one or more electrons. They have IE and gain in size as they gain electrons
2. A cation is a positively charged ion, formed by an atom giving away one or more of its electrons. They have low IE and get smaller as they lose electrons

Question 17

What is ionic bonding? provide examples

Answer 17

Ionic bonding is when one atom (usually a metal) gives up electron(s) to another atom (usually a non-metal)

Ionic bonds most commonly form between a metal and a non metal and have an electronegativity difference greater than 1.9

Question 18

What is metallic bonding? provide examples

Answer 18

Metallic bonding explain the characteristic of metals, metal atoms are surrounded by a ‘sea of electrons’ which are organised in a crystalline pattern

Bonding between positive metal ions and a sea of electrons is strong

Question 19

Describe covalent bonding (single, double and triple bonds)

Answer 19

Covalent bonding is when an atom shares an electron pair with another atom

When compared to ionic compounds, covalent compounds usually have a lower melting and boiling point, and have less of a tendency to dissolve in water. Covalent compounds can be in a gas, liquid, or solid state and do not conduct electricity or heat well

Single bonds is the sharing of 2 electrons, double bone is the sharing of 4 electrons, and triple bond is the sharing of 6 electrons

Question 20

Describe the polarity of bonds and compounds

Answer 20

Only when two atoms of the same element form a covalent bond are the shared electrons actually shared equally between the atoms. When atoms of different elements share electrons through covalent bonding, the electron will be drawn more toward the atom with the higher electronegativity resulting in a polar covalent bond

non-polar covalent bonds have an electronegativity difference of less than 0.5, polar covalent bonds have an electronegativity difference of 0.5-1.9, both are most likely to form between 2 non-metals or a non-metal and a metalloid

Ionic bonds have an electronegativity difference greater than 1.9 and most commonly form between a metal and a nonmetal

Question 21

What is a coordinate covalent bond?

Answer 21

A covalent bond in which one of the atoms contributes both of the electrons in the shared pair.