Unit 1: Matter, Chemical Trends, and Chemical Bonding

Question 1

As you go across a period, what happens to an atoms SIZE? And why?

Answer 1

The atom gets smaller, because:
1. there are more protons and electrons, but the same distance, and according to Coulombs Law, the larger the unlike charges, the greater the force of attraction.

Question 2

As you go down a group, what happens to an atoms SIZE? And why?

Answer 2

The atom gets larger, because:
1. More shielding
2. More energy levels, therefore more distance, and according to Coulomb’s Law, the greater the distance between unlike charges, the weaker the force of attraction.

Question 3

What is shielding?

Answer 3

“Electrons in filled energy levels between the nucleus and outer shell electrons shield the outer shell electrons somewhat from the effect of protons in the nucleus.”

In the same energy level, the shielding is the same.
The more energy levels between the nucleus and the outer electrons, the more shielding and the outer electrons are less attracted to the nucleus.

Question 4

Effective Nuclear Charge, (Zeff)

Answer 4

Effective nuclear charge, Zeff, is the net force of attraction between the electrons and the nucleus of the atom. It considers both the attractiveness of the nucleus, the energy level of the valence electrons and the shielding of valence electrons by core electrons.
We say that an atom such as Cl has a greater effective nuclear charge than Si since, even though the valence electrons are on the same energy level and amount of shielding is the same, Cl has MORE protons in the nucleus.

Question 5

Electronegativity

Answer 5

The electronegativity is the ability of an individual atom, when bonded to attract bonding electrons to itself.

Question 6

Delta EN range for something to be POLAR covalent:

Answer 6

0.5 - 1.8

Question 7

Inter- VS. Intra-Molecular forces