gen chem- Periodic Trends

Which of the following are most likely the first, second, and third ionization energies of Be?

A. 520, 7300, 11800 kJ/mol

B. 1680, 3370, 6050 kJ/mol

C. 500, 4560, 6910 kJ/mol

D. 900, 1760, 14800 kJ/mol

E. 800, 2430, 3660 kJ/mol

D

• ionization energy is the energy required to remove the most loosely bound valence electron from an atom, forming an ion

• represented by this equation: X + energy → X⁺ + electron

• Be’s e- configuration is 1s² 2s², meaning it has two valence e- in the 2s orbital

• the first ionization energy corresponds to removing one of the two valence e-

  • this requires only a moderate amnt of energy, as it brings Be closer to the stable e- configuration of a noble gas

• the second ionization energy involved removing the second valence e-

  • this requires more energy than the first b/c after losing the first e-, the remaining e- is more strongly attracted to the nucleus

  • removing this e- results in Be achieving a stable noble gas configuration

• the third ionization energy involved removing an electron from the stable noble gas configuration

  • this requires a very large amnt of energy b/c it is disrupting stability

  • so it is significantly higher than the first and second

Which of these elements will have a vigorous reaction in the presence of pure oxygen?

A. boron

B. sodium

C. germanium

D. sulfur

E. neon

B

• group 1 elements (alkali metals) and group 2 elements (alkaline earth metals) both react with pure oxygen, but with different intensities

• group 1 elements react more violently with oxygen

Na⁺_(g) + energy → Na²⁺_(g) + e^-

This equation is an example of which of the following?

A. first electron affinity

B. second electron affinity

C. first ionization energy

D. second ionization energy

D

• the equation shows the removal of an electron from Na+

• the second ionization energy of an element is the energy required to remove the second electron from a 1+ cation of the element

• A+B- is the energy released when an element gains its first/second e-

Which of the following atoms is the smallest?

A. Fe^-

B. Fe

C. Fe⁺

D. Fe²⁺

E. Fe³⁺

E

• when comparing the atomic radius of ions of the same element, those with fewer electrons are smaller

• Fe3+ has the fewest electrons with 23

• so it is the smallest due to the strongest effective nuclear charge per electrons and least electron repulsion

Rank the following species in order of increasing size:

I. Ca²⁺
II. S^2-
III. Cl^-
IV. Ar

A. II < III < I < IV
B. I < IV < III < II
C. III < I < II < IV
D. IV < III < I < II
E. they all have the same radius since they are isoelectronic

B

• atoms of an isoelectronic species contain the same number of electrons, so they have the same electron configuration

• for each atom, the atomic/ionic size is determined by the effective nuclear charge, which depends on the number of protons in the nucleus

• a higher number of protons results in a greater effective nuclear charge, which exerts a stronger attraction on the electrons and reduces the atomic or ionic size

• Ca2+ has the greatest # of protons (20 protons), making it the smallest, followed by Ar (18), etc.

An extracted pure compound appears silvery white and exhibits high conductivity to heat and electricity, yet it has a relatively low melting point. Which of the following elements could this compound be?

A. platinum

B. sodium

C. selenium

D. iodine

B

• the given compound exhibits high thermal and electrical conductivity, suggesting it is a metal

  • eliminate C+D b/c Se and I are nonmetals

• a low melting point indicates the metal is an alkali metal b/c they exhibit low melting points due to their weak metallic bonds

• Na is an alkali metal (group 1 element)

The decrease in atomic radius from left to right across a period on the periodic table can be best explained by

A. an increase in the number of protons

B. an increase in atomic mass

C. an increase in the number of inner shell electrons

D. an increase in the number of neutrons

E. a decrease in atomic mass

A

• across a period, atomic size decreases as the increasing number of protons strengthens the effect nuclear charge, pulling valence electrons closer to the nucleus

Which of the following statements represents a property of metals? 

A. produce binary hydrides that are insoluble in water

B. react readily to produce diatomic molecules

C. tend to form cations by loss of electrons

D. have high electron affinities

E. oxidize nonmetals in acidic solutions

C

• metals have low ionization energies and electronegativity, so they tend to lose electrons and form positively charged ions

Which of the following ions has the largest atomic radius?

A. Ca²⁺

B. Li⁺

C. S^2-

D. Cl^-

E. O^2-

C

• atomic radius of an ion is affected by two main factors: the number of electron shells (energy levels) and the effective nuclear charge

  1. # of e- shells: more electron shells result in a larger atomic radius b/c the e- are spread out over a larger physical space

  2. effective nuclear charge: a higher effective nuclear charge (more protons) results in a smaller atomic radius b/c the e- are pulled closer to the nucleus

• Ca2+, S2-, and Cl- all have 3 shells so need to compare protons

• S2- has the fewest protons so it has the largest atomic radius

Which of the following describes electron affinity?

A. the energy needed to remove an electron

B. the energy required to separate an ionic compound’s cations and anions

C. the energy absorbed when an electron is added to an atom

D. the force that attracts electrons toward the nucleus

E. the energy released when an atom gains an electron

E

• electron affinity is the energy released when an atoms gains an electron

• it follows the same periodic trend as electronegativity, increasing up and right

• A- ionization energy

• B- lattice energy

• D- effective nuclear charge

Which of the following has the longest bond length?

A. H-At

B. H-Br

C. H-Cl

D. H-F

E. H-I

A

• smaller atoms have shorter bond lengths b/c their nuclei can get closer together

• At has the largest atomic size so H-At has the longest bond length

Which element has the largest first ionization energy?

A. Sr

B. K

C. Br

D. F

E. O

D

Which of the following properties increases along with atomic number among elements of period five?

A. boiling point

B. atomic radius

C. electron affinity

D. vapor pressure

E. metallic character

C

• electron affinity is the energy released when an atom gains an e-

  • it increases moving up and right

• A+D- bp and vp do not follow a clear periodic trend

• B- atomic radium increases moving down and left

• E- metallic character measures the tendency for an atoms to lose its valence e- to form a cation; it increases moving down and left