Topic 3. Periodicity

Question 1

Who invented our modern periodic table, and what made their table special?

Answer 1

Dimitrij Mendelejev
He left gaps where elements had yet to be discovered. He also made predictions about these elements, and they were pretty accurate predictions.

Question 2

What are group 1 of the periodic table?

Answer 2

Alkili metals

Question 3

What are group 17 of the periodic table?

Answer 3

Halogens

Question 4

What are group 3-12 of the periodic table?

Answer 4

Transition metals

Question 5

What are group 18 of the periodic table?

Answer 5

Noble gases

Question 6

What is effective nuclear charge?

Answer 6

The attraction which valence electrons feel from the nucleus. It can be calculated by taking the number of protons minus the number of electrons in the inner shells. The higher effective nuclear charge, the stronger the attraction on the valence electrons.

Question 7

What is atomic radii?

Answer 7

The atomic radii is half the distance between the nuclei of two bonded atoms of the same element.
* Going down a group, the atomic radii will increase as the valence electrons get further away from the nucleus.
* Going across a period, the atomic radii will decrease as the number of protons (and the nuclear charge) increases. Since the extra electrons are added to the same energy level, the attraction from the nucleus on that level will increase.

Question 8

Ionic radii of cations

Answer 8

Cations have lost electrons, and therefore have a stronger attraction from the nucleus, thus they are smaller than the parent atom. Across a period the ions contain the same number of electrons, but an increasing number of protons, so the ionic radius will decrease.

Question 9

Ionic radii of anions

Answer 9

Anions have gained electrons, and therefore have a weaker attraction from the nucleus, thus they are bigger than the parent atom. Across a period the ions contain the same number of electrons, but an increasing number of protons, so the ionic radius will decrease.

Question 10

How does ionisation energy change when going down a group?

Answer 10

The ionisation energy will decrease when going down a group

Question 11

How does ionisation energy change when going across a period?

Answer 11

The ionisation energy will increase when going across a period.

Question 12

What is electron affinity?

Answer 12

Electron affinity is the energy change when one mole of electrons is added to one mole gaseous atoms to form one mole of gaseoys ions.

Question 13

What is electronegativity?

Answer 13

Electronegativity is a relative measure of the attraction that an atom has for a shared pair of electrons in a covalent bond. As the size of the atom deceases the electronegativity increases.
* Going down a group the size of atoms increase, thus electronegativity decreases
* Going across a period the size of atoms decrease, thus electronegativity increases

Question 14

How does melting point vary when going down a group?

Answer 14

• When going down group 1, the melting point will decrease due to the metallic bond gets weaker
• When going down group 17, the melting point will increase due to London forces becoming stronger

Question 15

What are the chemical properties of alkali metals?

Answer 15

• They have 1 valence electron
• They are reactive, soft metals
• The further down the group the more reactive they become

Question 16

What are the chemical properties of halogens?

Answer 16

• They have 7 valence electrons
• The reactivity decreases going down the group
• In their pure form they exist as diatomic molecules

Question 17

What is characteristic of metals?

Answer 17

• Shiny surface
• Good conductors of heat and electricity
• Malleable and ductile

Question 18

What is characteristic of metalloids?

Answer 18

• Semiconductor
• Powdered, not shiny

Question 19

What is characteristic of non-metals?

Answer 19

• Gases or powdered solids
• Do not conduct electricity