Periodic Trends, Atomic Properties, and Reactivity in Chemistry

What is the Effective Nuclear Charge (Zeff)?

A measure of the attraction between outer electrons and the nucleus, calculated as Zeff = Z - S, where Z is the atomic number and S is the shielding constant.

How does Zeff change across a period?

Zeff increases going to the right in a given period due to an increase in the number of protons while the number of inner core electrons remains constant.

What is the bonding radius?

The bonding radius is defined as half the distance between covalently bonded atomic nuclei.

What is the nonbonding radius?

The nonbonding radius (van der Waals radius) is the closest approach of another nonbonded atom and is not a constant value.

How do atomic radii change down a group?

Radii increase going down a group because the electron energy level increases while Zeff remains relatively constant.

What happens to atomic radii across a period?

Radii decrease going across a period due to increasing Zeff which pulls electrons closer to the nucleus.

What is the trend for cation and anion sizes compared to parent atoms?

Cations are smaller than parent atoms, while anions are larger than parent atoms.

What is ionization energy?

Ionization energy (I) is the energy required to remove the highest energy electron from an atom or ion in its ground state as a gas.

How does ionization energy change across a period?

Ionization energy generally increases going across a period due to increasing Zeff.

How does ionization energy change down a group?

Ionization energy generally decreases going down a group as Zeff remains constant while electron energy increases.

What is electron affinity?

Electron affinity is the energy change resulting from adding an electron to an atom in its gas phase, which can be positive or negative.

What is the trend for electron affinity across a period?

Electron affinity generally becomes more negative going across a period.

What are the properties of metals?

Metals are usually shiny, malleable, ductile, and good conductors of heat and electricity.

What are the properties of nonmetals?

Nonmetals are usually dull, brittle, and poor conductors of heat and electricity.

What are metalloids?

Metalloids have characteristics of both metals and nonmetals, such as being shiny yet brittle.

What are alkali metals?

Alkali metals are highly reactive, soft solids that do not occur in pure forms in nature and react violently with water.

What are alkaline earth metals?

Alkaline earth metals are moderately reactive solids that do not occur in pure form in nature and have higher densities than alkali metals.

What are chalcogens?

Chalcogens include nonmetals (O, S, Se), a metalloid (Te), and a metal (Po), with reactivity ranging from highly reactive (O) to poorly reactive (Po).

What are halogens?

Halogens are highly reactive nonmetals that react with metals to form salts and include F2, Cl2, Br2, and I2.

What are noble gases?

Noble gases are nonreactive, monoatomic gases with filled valence shells, making them stable.

What is the significance of isoelectronic ions?

Isoelectronic ions and atoms have the same number of electrons, affecting their radii as Zeff increases.

What is the relationship between electronegativity and Zeff?

Electronegativity generally increases as Zeff increases, meaning elements hold bonding electrons more closely.

What is the trend for electronegativity down a group?

Electronegativity generally decreases going down a group.

What is the trend for electronegativity across a period?

Electronegativity generally increases going across a period.

What is the significance of the transition between elements in terms of ionization energy?

There is a drop in ionization energy between the last transition metal and the next element due to a significant energy jump in the p orbital.

What happens when alkali metals react with water?

Alkali metals react violently with water to produce basic solutions and hydrogen gas.

What is the chemical reaction for sodium reacting with water?

2 Na(s) + 2 H2O(ℓ) → 2 NaOH(aq) + H2(g)