2. Periodic Table of Elements

Question 1

What is electron configuration?

Answer 1

Describes how electrons are arranged in an atom’s orbitals.
Determined by four quantum numbers.
Each orbital holds max 2 electrons with opposite spins.

Question 2

What principles guide electron configuration?

Answer 2

1. Aufbau Principle:
   Electrons fill lower-energy orbitals first, then higher ones.
2. Pauli Exclusion Principle:
   No two electrons in an atom can have the same four quantum numbers.
3. Hund’s Rule:
   Electrons fill orbitals singly first, then pair up for maximum stability.

Question 3

How are orbitals filled?

Answer 3

s orbitals hold 2 electrons.
p orbitals hold 6 electrons.
d orbitals hold 10 electrons.
f orbitals hold 14 electrons.

Question 4

What are paramagnetic & diamagnetic substances?

Answer 4

Paramagnetic: Have unpaired electrons, attracted to a magnetic field.
Diamagnetic: Have all paired electrons, repelled by a magnetic field.

Question 5

What is the electron shielding effect?

Answer 5

Inner electrons shield outer electrons from nuclear attraction.
Reduces nuclear pull on higher-energy electrons.
Explains exceptions in electron configurations (e.g., copper, chromium).

Question 6

What is noble gas notation?

Answer 6

Uses previous noble gas in brackets to shorten electron configurations.
Example: Nickel (Ni) → [Ar] 3d⁸ 4s².
Helps focus on valence electrons, which determine chemical reactivity.

Question 7

How is the periodic table arranged?

Answer 7

Elements ordered by atomic number (left to right, top to bottom).
Rows (Periods): Correspond to the highest energy level of electrons.
Columns (Groups): Indicate outermost electron configuration.

Question 8

Why do periods have different lengths?

Answer 8

First period: Only 2 elements (1s orbital fills up).
Second period: 8 elements (2s and 2p orbitals fill up).
Periods lengthen as more subshells (d, f) are introduced.

Question 9

What do groups tell us?

Answer 9

Elements in the same group share similar chemical properties.
Group number = Number of valence electrons (except transition metals).
Example: Group 1 → 1 valence electron, Group 2 → 2 valence electrons.

Question 10

What are periodic trends?

Answer 10

1. Atomic Radius:
   Decreases across a period (→) due to stronger nuclear charge.
   Increases down a group (↓) due to additional energy levels.
2. Ionization Energy:
   Increases across a period (→) (harder to remove electrons).
   Decreases down a group (↓) (easier to remove electrons).
3. Electron Affinity:
   Increases across a period (→) (atoms more willing to gain electrons).
   Decreases down a group (↓).

Question 11

What is Effective Nuclear Charge (Zeff)?

Answer 11

Zeff = Attraction between nucleus & electrons after accounting for shielding.
Increases across a period (more protons pull electrons closer).
Decreases down a group (more electron shielding reduces pull).

Question 12

What is Electron Shielding?

Answer 12

Inner electrons “shield” outer electrons from full nuclear attraction.
Causes exceptions in periodic trends (e.g., transition metals, noble gases).

Question 13

What are Noble Gases?

Answer 13

Group 18 elements (He, Ne, Ar, Kr, Xe, Rn).
Least reactive due to full valence shell.
High ionization energy, low electron affinity.

Question 14

What is Electron Affinity vs. Ionization Energy?

Answer 14

Ionization Energy: Energy required to remove an electron.
Electron Affinity: Energy released when an electron is gained.

Question 15

How are elements classified by properties?

Answer 15

Metals (blue): Good conductors, malleable, ductile.
Nonmetals (orange): Poor conductors, brittle, various states.
Metalloids (gray): Have properties between metals & nonmetals.

Question 16

Special Element Groups

Answer 16

Alkali Metals (Group 1): Highly reactive, form +1 ions.
Alkaline Earth Metals (Group 2): Less reactive, form +2 ions.
Halogens (Group 17): Highly reactive nonmetals, form -1 ions.

Question 17

What do Molecular Formulas Tell Us?

Answer 17

Show proportions & number of atoms in a molecule.
Example:
Water (H₂O) → 2 hydrogen, 1 oxygen.
Ammonia (NH₃) → 1 nitrogen, 3 hydrogen.
Ionic compounds (e.g., NaCl) do not form molecules but 3D structures.

Question 18

Naming Binary Ionic Compounds

Answer 18

Metal (cation) + Nonmetal (anion with -ide suffix)
NaCl → Sodium chloride
MgO → Magnesium oxide
For metals with multiple charges, use Roman numerals:
FeO → Iron(II) oxide
Fe₂O₃ → Iron(III) oxide

Question 19

Naming Molecular (Covalent) Compounds

Answer 19

Use prefixes for number of atoms:
CO₂ → Carbon dioxide
N₂O₅ → Dinitrogen pentoxide
Prefixes:
1 = Mono-
2 = Di-
3 = Tri-
4 = Tetra-
5 = Penta-, etc.

Question 20

Properties of Representative Elements

Answer 20

Trends exist but have exceptions.
Groups 1A & 2A → Similar properties within each group.
Higher groups → More variation in properties.
Hydrogen is unique → Not part of Group 1A due to distinct behavior.