Periodic Trends, Alkali Metals, and Halogens

Vocabulary flashcards covering first ionization energy, electron affinity, electronegativity trends, properties and reactions of alkali metals (Group 1), and halogens (Group 17).

First Ionization Energy

The amount of energy needed to remove an electron (just $1$) from a neutral atom in the gaseous state.

Group Trend of Ionization Energy

Ionization energy decreases as you move down a column because elements have more shells, placing valence electrons further away from the nucleus, resulting in less attraction and making electrons easier to remove.

Period Trend of Ionization Energy

Ionization energy increases as you move from left to right across a period because valence electrons are more tightly held due to increasing effective nuclear charge (same number of shells with an increasing number of protons in the nucleus).

Electronegativity

A relative value (with no units) that measures the ability of an atom (its nucleus) to attract a bonding pair of electrons, reflecting how tightly an electron is held.

Periodic Trends of Electronegativity

Decreases as you move down any group (due to increasing atomic radius and atoms being less willing to accept electrons) and increases as you move across a period from left to right (due to increasing effective nuclear charge).

Francium ($Fr$)

The element with the lowest electronegativity value ($0.7$).

Fluorine ($F$) Electronegativity

The element that possesses the highest electronegativity value ($4.0$).

Noble Gases (Electronegativity)

Elements that have complete $p$ shells, meaning they are not willing to attract another electron and therefore have no electronegativity.

Liquid ($l$) vs. Aqua ($aq$)

Liquid refers to a substance (such as water) in its liquid state, whereas aqua (aqueous) means a substance is dissolved in water.

Alkali Metals

Group 1 elements ($Li$, $Na$, $K$, $Rb$, $Cs$, $Fr$) that are chemically reactive because they lose electrons.

Lithium ($Li$)

A Group 1 metal that is solid, cuttable with a knife, grayish-whiteish, has a shiny surface before oxidizing, is the lightest metal, and floats on the water surface and bubbles.

Reaction of Lithium with Water

$2Li_{(s)} + 2H_2O_{(l)} \rightarrow 2LiOH_{(aq)} + H_{2(g)}$, producing lithium hydroxide with a $\text{pH} > 7$.

Lithium Flame Test and Applications

Produces a red flame; used in batteries, H-bombs, and medicine for manic depression.

Sodium ($Na$)

An alkali metal that is softer than lithium, solid, shiny silver, floats on the surface of water, and reacts directly on the surface.

Reaction of Sodium with Water

$2Na_{(s)} + 2H_2O_{(l)} \rightarrow 2NaOH_{(aq)} + H_{2(g)}$, forming sodium hydroxide.

Sodium Flame and Common Salt

Produces an orange flame; present in table salt as $NaCl$ ($Na^+$).

Potassium ($K$)

A malleable, solid alkali metal that reacts with $H_2O$, floats, and exhibits a lilac flame.

Reaction of Potassium with Water

$2K_{(s)} + 2H_2O_{(l)} \rightarrow 2KOH_{(aq)} + H_{2(g)}$.

Element Reactivity Basis

Reactivity depends on first ionization energy; alkali metals react by losing electrons, whereas halogens react by gaining electrons.

Halogens

Group 17 diatomic elements (consisting of $2$ atoms) that react by gaining electrons.

Fluorine ($F_2$)

A diatomic halogen that is a pale yellow gas at room temperature (dark yellow when condensed) and extremely reactive because it has the highest electronegativity.

Reaction of Fluorine with Iron

$3F_{2(g)} + 2Fe_{(s)} \rightarrow 2FeF_{3(s)}$ (producing iron fluoride).

Chlorine ($Cl_2$)

A greenish-yellow gas that is heavier than air (stays down), very poisonous, and less reactive than fluorine.

Reaction of Chlorine with Aluminum

$2Al_{(s)} + 3Cl_{2(g)} \rightarrow 2AlCl_{3(s)}$.

Bromine ($Br_2$)

A red-colored liquid that produces orange fumes and is less reactive than $Cl_2$.

Reaction of Bromine with Aluminum

$2Al_{(s)} + 3Br_{2(l)} \rightarrow 2AlBr_{3(s)}$.

Iodine ($I_2$)

A blackish solid that emits purple fumes and is less reactive than $F_2$, $Cl_2$, and $Br_2$.

Reaction of Iodine with Aluminum

$2Al_{(s)} + 3I_{2(s)} \rightarrow 2AlI_{3(s)}$.