3.1 - The Periodic Table: Classification of Elements

Question 1

Group:

Answer 1

Elements with the same number of valence electrons and therefore similar chemical and physical properties; a vertical column of elements.

Question 2

Period:

Answer 2

Elements with the same outer shell; a horizontal row of elements.

Question 3

Which group are the alkali metals?

Answer 3

Group 1

Question 4

List 3 physical properties of alkali metals

Answer 4

• Soft solids
• Very reactive
• React with water to form a basic solution of the metal hydroxide + hydrogen gas.

Question 5

Which group are the alkaline earth metals?

Answer 5

Group 2

Question 6

List 3 physical properties of alkaline earth metals

Answer 6

• Most abundant metal on the planet
  -not as reactive as alkali metals
• higher density and melting point than alkali metals

Question 7

Which group are the halogens?

Answer 7

Group 7

Question 8

List 3 physical properties of Halogens

Answer 8

• Gases (F and Cl), liquids (Br) and solids (I)
• Very reactive non-metal
• Form salts with alkaline metals

Question 9

Which group are the noble gases?

Answer 9

Group 0 (or 8)

Question 10

List 3 physical properties of noble gases

Answer 10

• Almost non-reactive
• Sometimes called rare gases or inert gases
• Gases at room temperature

Question 11

List all 5 periodic trends

Answer 11

• Atomic radius
• Ionic radius
• First ionization energy
• Electronegativity
• Melting point

Question 12

State the trend for atomic radius

Answer 12

Increases down a group:
- Electrons are added to energy levels farther away from the nucleus.
- Inner electrons shield the outer electrons from the positive charge of the nucleus.

Decreases across a period:
- As the protons increase, the positive charge increases; the pull increases

Question 13

State the trend for ionic radius

Answer 13

Increases down a group:
- Outer electrons are further from the nucleus

Decreases across a period:
- The ions contain the same number of electrons but an increasing number of protons, so the ionic radius decreases.

Question 14

Define first ionization energy

Answer 14

The energy required to remove one outer electron from a gaseous atom.

Question 15

State the trend for first ionization energy

Answer 15

Decreases down a group:
- Electrons in higher electronic shells are further away from the positive charge of the nucleus and therefore easier to remove.
- As the distance to the nucleus increases, electrostatic force is reduced. The shielding effect also reduces the charge.

Increases across a period:
- The increasing charge in the nucleus as you move across a period exerts greater electrostatic force on the electrons; it requires more energy to remove an electron.

Question 16

Define electronegativity

Answer 16

A measure of a tendency of an atom to attract electrons.

Question 17

State the trend for melting point

Answer 17

Group 1:
- Decreases down a group
Group 2:
- Decreases down a group
Group 7:
- Increases down a group
Group 0 (or 8):
- Increases down a group

Question 18

State the trend for electronegativity

Answer 18

Decreases down a group:
- The larger radius means the electrons are farther away from the nucleus, leading to decreased electrostatic attraction, so decreased electronegativity.
- Shielding effect

Increases across a period:
- Nuclear charge is increasing, atomic radius is decreasing; attractive electrostatic force that the nucleus can exert on another electron increases.

Question 19

State 4 chemical properties of alkali metals

Answer 19

• React by losing one electron
• Reactivity increases down the group as the electron is in higher shell levels; less energy is required to remove it.
• React with water to form a metal hydroxide solution and hydrogen gas
  React with halogens to form ionic salts

Question 19

State 3 chemical properties of halogens

Answer 19

• React by gaining one electron
  Reactivity decreases down the group as the valence electrons are increasingly at higher electronic shells and further from the nucleus. Plus shielding.
• In displacement reactions, the more reactive (higher in the group) elements replace the less reactive ones.

Question 20

Describe the test for halide ions

Answer 20

Adding silver nitrate solution to a solution helps detect for halides.
AgCl = White
AgBr = Cream
AgI = Yellow