Understanding the Map of Elements
The periodic table isn't random - it's organized by electron configuration! Elements in the same column (group) have similar properties because they have the same number of valence electrons.
The periodic table is divided into four blocks based on which sublevel is being filled:
Groups 1-2 (plus H and He)
Filling: ns¹ or ns²
Includes: Alkali metals, Alkaline earth metals
Groups 13-18
Filling: np¹ through np⁶
Includes: Halogens, Noble gases, many nonmetals
Groups 3-12
Filling: (n-1)d¹ through (n-1)d¹⁰
Includes: Transition metals
Bottom two rows
Filling: (n-2)f¹ through (n-2)f¹⁴
Includes: Lanthanides (4f), Actinides (5f)
Problem: Groups 13-18 form the area where which electron sublevels are being filled?
Solution: Groups 13-18 are the p-block, so p sublevels are being filled.
(Note: The s electrons are already filled before the p sublevel starts)
Elements: Li, Na, K, Rb, Cs, Fr
Valence: ns¹ (1 valence electron)
Typical Ion: +1 (loses 1 e⁻)
Properties: Very reactive metals, soft, low density
Elements: Be, Mg, Ca, Sr, Ba, Ra
Valence: ns² (2 valence electrons)
Typical Ion: +2 (loses 2 e⁻)
Properties: Reactive metals, harder than Group 1
Elements: F, Cl, Br, I, At
Valence: ns²np⁵ (7 valence electrons)
Typical Ion: -1 (gains 1 e⁻)
Properties: Very reactive nonmetals
Elements: He, Ne, Ar, Kr, Xe, Rn
Valence: ns²np⁶ (8 valence, full outer shell)
Typical Ion: 0 (rarely form ions)
Properties: Extremely unreactive, colorless gases
Examples: Fe, Cu, Zn, Ag, Au, Pt
Filling: d sublevels
Properties: Can form multiple ions (Fe²⁺ and Fe³⁺), often colored compounds, good conductors
Problem: Which group contains the alkali metals?
Answer: Group 1
Note: Hydrogen is in Group 1 but is NOT an alkali metal - it's a nonmetal!
Problem: Which element is NOT a noble gas: Ra, Xe, He, or Ar?
Answer: Ra (Radium)
Ra is in Group 2 (alkaline earth metals). Noble gases are in Group 18.
Properties of elements follow predictable patterns across the periodic table.
The size of an atom (distance from nucleus to outermost electrons)
← Decreases across period →
More protons pull electrons closer
↓ Increases down group ↓
More energy levels = bigger atom
Largest atoms: Bottom-left (Cs, Fr)
Smallest atoms: Top-right (He excluded, so F)
Problem: In Group 15, which element has the smallest atomic radius?
Options: Bi, P, As, N
Solution: Atomic radius decreases going UP a group.
Order from largest to smallest: Bi > As > P > N
Answer: N (Nitrogen) - it's at the top of Group 15
How "metal-like" an element is (shiny, conductive, loses electrons easily)
← Decreases across period →
Elements become more nonmetallic
↓ Increases down group ↓
Easier to lose electrons = more metallic
Most metallic: Bottom-left (Cs, Fr)
Least metallic: Top-right (F)
Problem: In Group 14, which element is the MOST metallic?
Options: C, Si, Ge, Sn
Solution: Metallic character increases going DOWN a group.
Answer: Sn (Tin) - it's at the bottom of the listed options
(Pb is even lower and more metallic, but wasn't an option)
| Property | Across Period (→) | Down Group (↓) |
|---|---|---|
| Atomic Radius | Decreases | Increases |
| Metallic Character | Decreases | Increases |
| Ionization Energy | Increases | Decreases |
| Electronegativity | Increases | Decreases |
| Category | Reactivity | Why? |
|---|---|---|
| Noble Gases (18) | LEAST reactive | Full outer shell - stable! |
| Alkali Metals (1) | VERY reactive | Only 1 electron to lose |
| Halogens (17) | VERY reactive | Only 1 electron needed to fill shell |
Problem: Which group contains the LEAST reactive elements?
Options:
Answer: d. Noble Gases
Noble gases have full outer shells and rarely react with anything.
| Group 1 | Alkali Metals - 1 valence electron, +1 ion |
| Group 2 | Alkaline Earth Metals - 2 valence electrons, +2 ion |
| Groups 3-12 | Transition Metals - d-block, variable charges |
| Group 17 | Halogens - 7 valence electrons, -1 ion |
| Group 18 | Noble Gases - 8 valence electrons (2 for He), unreactive |
| Lanthanides/Actinides | f-block - filling f sublevels |