Question

answer the following questions.

1. explain why an atom with a high ionization-energy value is not likely to form a positive ion.

1. what is the period trend for atomic radius? why?

1. what is the group trend in the first ionization energies? why?

1. what element has the highest value for electronegativity?

1. what are period and group trends in electronegativities?

1. what are valence electrons and how many valence electrons does silicon have?

understanding main ideas
circle the letter of the choice that best completes the statement or answers the question.

1. elements in the same group have similar chemical properties because

a. their atoms are about the same size. c. they have the same number of valence electrons.
b. they have a similar atomic mass. d. they have a diagonal relationship.

1. which of the following statements does not describe the alkali metals?

a. most are shiny gray solids that are very soft.
b. they easily gain an electron to form ions with a charge of -1.
c. they are not found uncombined in nature.
d. they react with water to form alkaline solutions.

Explanation:

• Question 33: Ionization energy is the energy required to remove an electron from an atom. A high ionization - energy value means a large amount of energy is needed to remove an electron. Since forming a positive ion requires losing an electron, an atom with high ionization energy is reluctant to lose an electron.
• Question 34: In a period (row) of the periodic table, the atomic radius decreases from left to right. This is because as we move from left to right in a period, the number of protons in the nucleus increases (increasing the nuclear charge), and electrons are added to the same principal energy level. The increased nuclear charge pulls the electrons closer to the nucleus.
• Question 35: In a group (column) of the periodic table, the first ionization energy decreases from top to bottom. As we move down a group, the atomic size increases (more electron shells are added). The outermost electrons are farther from the nucleus and are less strongly attracted by the nucleus, so less energy is required to remove them.
• Question 36: Fluorine has the highest value for electronegativity. Electronegativity is the ability of an atom to attract electrons in a chemical bond. Fluorine has a small atomic size and a high nuclear charge, which makes it very effective at attracting electrons.
• Question 37:
• Period trend: Electronegativity increases from left to right in a period. The increasing nuclear charge (more protons) and relatively constant shielding (electrons in the same principal energy level) make atoms more able to attract electrons.
• Group trend: Electronegativity decreases from top to bottom in a group. The increasing atomic size (more electron shells) and increased shielding effect (inner electrons shielding the outermost electrons from the nucleus) reduce the ability of atoms to attract electrons.
• Question 38: Valence electrons are the electrons in the outermost shell of an atom that are involved in chemical bonding. Silicon has an atomic number of 14. Its electron configuration is \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{2}\). The outermost shell (the third shell) has 4 electrons. So, silicon has 4 valence electrons.
• Question 39: Elements in the same group have similar chemical properties because they have the same number of valence electrons. Valence electrons are responsible for an element's chemical behavior (e.g., how it bonds with other elements).
• Question 40: Alkali metals (Group 1 elements) easily lose an electron (not gain) to form ions with a charge of + 1. For example, sodium (\(Na\)) loses one electron to form \(Na^{+}\).

Answer:

• 33: A high ionization - energy value means a large amount of energy is needed to remove an electron. Since forming a positive ion requires losing an electron, an atom with high ionization energy is not likely to form a positive ion.
• 34: In a period, atomic radius decreases from left to right. Because the nuclear charge increases (more protons) and electrons are in the same principal energy level, pulling electrons closer.
• 35: In a group, first ionization energy decreases from top to bottom. As atomic size increases (more shells), outermost electrons are less strongly attracted.
• 36: Fluorine.
• 37:
• Period: Increases from left to right (due to increased nuclear charge and constant shielding).
• Group: Decreases from top to bottom (due to increased atomic size and shielding).
• 38: Valence electrons are outermost - shell electrons involved in bonding. Silicon has 4 valence electrons.
• 39: c. they have the same number of valence electrons.
• 40: b. They easily gain an electron to form ions with a charge of - 1.