chapter three: periodic properties

What is the modern periodic law?

The properties of elements repeat periodically when arranged by increasing atomic number.

Why do periodic properties repeat?

Repeating electron configurations create repeating valence-electron arrangements and properties.

What is Coulomb's law?

It describes attraction or repulsion between charged particles; attraction gets weaker as distance increases.

What is shielding?

Inner electrons reduce the nucleus's attraction felt by outer electrons.

What is effective nuclear charge (Z_eff)?

The net positive nuclear attraction an electron experiences after shielding.

How does nuclear charge (Z_eff ) change across a period?

It generally increases from left to right.

What is penetration?

How closely an electron in an orbital can approach the nucleus.

Which orbitals have the greatest penetration?

s > p > d > f.

Why does penetration matter?

Greater penetration means stronger nuclear attraction and affects orbital energy.

What is a quantum number?

A number describing a particular aspect of an electron's state.

What does the principal quantum number n describe?

The main energy level or shell.

What does the angular momentum quantum number l describe?

The subshell and orbital shape.

What l values correspond to s, p, d, and f?

s = 0, p = 1, d = 2, f = 3.

What does the magnetic quantum number m_l describe?

An orbital's orientation within a subshell.

What values can m_l have?

From −l through 0 to +l.

How many orbitals are in s, p, d, and f?

1, 3, 5, and 7, respectively.

How many electrons can s, p, d, and f hold?

2, 6, 10, and 14, respectively.

How many electrons can one orbital hold?

2 electrons, with opposite spins.

What is an orbital?

A region of high probability for finding an electron, not a fixed path.

What are the general shapes of s and p orbitals?

s is spherical; p has two lobes and is commonly drawn like a dumbbell.

What is the general shape of d orbitals?

Most have four lobes; one has a ring and two lobes.

What is the Pauli exclusion principle?

An orbital holds at most 2 electrons, and they must have opposite spins.

What is Hund's rule?

Equal-energy orbitals fill singly with parallel spins before pairing.

What is the Aufbau principle?

Lower-energy orbitals fill before higher-energy orbitals.

What is an electron configuration?

It shows how an atom's electrons are distributed among orbitals.

How does the periodic table connect to electron configuration?

Periods show the highest occupied energy level; blocks show the subshell being filled.

Where are metals, nonmetals, and metalloids found?

Metals are mainly left/center; nonmetals upper-right; metalloids near the staircase.

What is an ion?

A particle with unequal numbers of protons and electrons.

What is a cation?

A positively charged ion formed by losing electrons.

What is an anion?

A negatively charged ion formed by gaining electrons.

What determines an element's identity?

The number of protons.

What is the octet idea?

Main-group atoms often gain, lose, or share electrons to reach a stable noble-gas-like valence shell.

What is atomic radius?

A measure of an atom's size.

What is the general trend for atomic radius?

It increases down and to the left.

Why does atomic radius decrease across a period?

Increasing Z_eff pulls electrons closer while they remain in the same main energy level.

Why does atomic radius increase down a group?

Additional shells place valence electrons farther from the nucleus and increase shielding.

What two factors mainly explain atomic size?

Z_eff and electron distance from the nucleus.

What happens to shielding down a group?

It increases because additional inner shells are added.

What is ionic radius?

A measure of an ion's size.

How does a cation compare with its neutral atom?

A cation is generally smaller because it lost electrons.

How does an anion compare with its neutral atom?

An anion is generally larger because added electrons increase repulsion.

What is an isoelectronic species?

A species with the same number of electrons as another species.

How do you compare sizes of isoelectronic species?

More protons means stronger attraction and a smaller radius.

What is ionization energy?

The energy required to remove an electron from a gaseous atom or ion.

What is the general trend for ionization energy?

It increases up and to the right.

Why does ionization energy increase across a period?

Ionization energy is the energy needed to remove an electron from a gaseous atom or ion. It increases as you move from left to right across a period for two main reasons:

• Increasing Nuclear Charge (Z): As you move across a period, protons are added to the nucleus one by one. This makes the positive pull of the nucleus stronger.

• Constant Shielding: Electrons are added to the same outer shell (or energy level). The inner core-electron shielding stays roughly the same, so it does not block the growing positive charge

Why does ionization energy decrease down a group?

Outer electrons are farther away and more shielded.

What does a large jump in successive ionization energies indicate?

All valence electrons have been removed; the next electron is a core electron.

How do successive ionization energies reveal valence electrons?

The number of electrons removed before the huge jump equals the number of valence electrons.

What is electron affinity?

The energy change associated with adding an electron to a gaseous atom.

What is the general trend for electron affinity?

Attraction for an added electron generally increases toward the upper-right, with exceptions.

What is metallic character?

How strongly an element displays metallic behavior, especially its tendency to lose electrons.

What is the general trend for metallic character?

It increases down and to the left.

What is the relationship between atomic radius and ionization energy?

They generally have opposite trends: larger atoms have lower ionization energy.

What three ideas explain most periodic trends?

Nuclear charge, shielding, and electron distance from the nucleus.

What happens when transition metals form cations?

ns electrons are generally removed before (n−1)d electrons.

What is Fe's electron configuration?

[Ar] 4s² 3d⁶.

What is Fe²⁺'s electron configuration?

[Ar] 3d⁶.

What is Fe³⁺'s electron configuration?

[Ar] 3d⁵.

What does paramagnetic mean?

The species has one or more unpaired electrons.

What does diamagnetic mean?

All electrons are paired.

How many unpaired electrons does p³ have?

3.

How many unpaired electrons does p⁴ have?

2.

How many unpaired electrons does p⁵ have?

1.

How many unpaired electrons does p⁶ have?

0.

How many unpaired electrons does d⁵ have?

5.

How many unpaired electrons does d⁶ have?

4.

What are the three principles used for electron configurations?

Aufbau, Pauli exclusion, and Hund's rule.

How do you write an electron configuration from the periodic table?

Count electrons, fill orbitals in increasing energy, and follow Aufbau, Pauli, and Hund.

How do you write noble-gas shorthand?

Use the preceding noble gas in brackets, then write the remaining electrons.

How do you write an ion's electron configuration?

Start with the neutral atom; add electrons for anions or remove them for cations.

How do you write a transition-metal cation configuration?

Remove ns electrons before (n−1)d electrons.

How do you determine main-group valence electrons from configuration?

Count electrons in the outermost occupied principal energy level.

How do you determine an ion's charge from protons and electrons?

Subtract electrons from protons.

How do you determine which atom is larger?

Use the atomic-radius trend: down and to the left.

How do you determine which atom has greater ionization energy?

Use the ionization-energy trend: up and to the right.

How do you compare isoelectronic ions?

Confirm equal electrons, then compare protons; more protons means smaller radius.

How do you identify valence electrons from successive ionization energies?

Find the huge jump; electrons removed before it are the valence electrons.

How do you determine whether an atom is paramagnetic?

Write its orbital diagram and look for unpaired electrons.

What should you do if two electrons in one orbital have the same spin?

Correct it to opposite spins; otherwise it violates Pauli exclusion.

What should you do if p electrons pair before each p orbital has one electron?

Spread them out first; otherwise it violates Hund's rule.

What is the fastest way to check an electron configuration?

Count electrons, check filling order, Pauli, and Hund's rule.

An atom has 13 electrons. What element is it?

Aluminum (Al).

An atom has 17 electrons and is neutral. What element is it?

Chlorine (Cl).

An ion has 18 electrons and a +1 charge. How many protons does it have?

19 protons; the element is potassium (K).

An ion has 18 electrons and a −1 charge. How many protons does it have?

17 protons; the element is chlorine (Cl).

What is the electron configuration of Na⁺?

1s² 2s² 2p⁶, or [Ne].

What is the electron configuration of Mg²⁺?

1s² 2s² 2p⁶, or [Ne].

What is the electron configuration of F⁻?

1s² 2s² 2p⁶, or [Ne].

What is the electron configuration of Cl⁻?

[Ar].

What is the electron configuration of O²⁻?

[Ne].

What is the electron configuration of K⁺?

[Ar].

Which is larger, K or K⁺?

K, because K⁺ lost its outermost electron shell.

Which is larger, F or F⁻?

F⁻, because gaining electrons increases electron-electron repulsion.

Which has greater ionization energy, Na or Cl?

Cl, because ionization energy generally increases toward the upper-right.

Which has greater atomic radius, Na or Cl?

Na, because atomic radius decreases across a period.

Which has greater metallic character, Na or Cl?

Na, because metallic character decreases across a period.

Which has greater ionization energy, Li or K?

Li, because ionization energy decreases down a group.

Which has greater atomic radius, Li or K?

K, because atomic radius increases down a group.

Which has greater metallic character, Li or K?

K, because metallic character increases down a group.