Fall 2024 Finals Review Part 2

How many valence electrons are represented here?

• 16

• 2

• 6

• 8

Answer explanation

Valence electrons are the electrons in the outermost shell (orbit). The diagram shows there are 6 electrons.

Tags

NGSS.HS-PS1-1

Which of the following will form an ion with a charge of -2?

• Neon (Ne)

• Selenium (Se)

• Calcium (Ca)

• Lithium (Li)

Answer explanation

An ion charge of -2 results from an atom gaining 2 electrons to satisfy the Octet Rule (8 valence electrons). Among the choices, selenium (Se) is the one that has 6 valence electrons. To get to octet, Se gains 2 electrons and acquires a -2 charge.

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

This could be the Lewis symbol of the following EXCEPT:

• Mg

• He

• Na

• Ra

Answer explanation

The Lewis symbol shows two dots. These correspond to 2 valence electrons, typical of Group 2 elements like Mg and Ra. Helium (He) only has 2 electrons so the Lewis symbol can also represent He. Na is in Group 1 and it only has 1 valence electron, so it's Lewis symbol should only have 1 dot.

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

Ionic bond results from the

• attraction of shared electrons to the atom

• transfer of electrons from the metal to the nonmetal

• transfer of electrons from the nonmetal to the metal

• sharing of electrons

Which of the following will form a covalent bond?

• K and H

• Cu and Zn

• H and Br

• Ca and I

Answer explanation

A covalent bond results from sharing of electrons between NONMETALS. Among the answer choices, H and Br are the only pair of nonmetals.

Tags

NGSS.HS-PS1-2

Which of the following will form an ionic bond?

• H and O

• O and N

• Ca and Zn

• Ca and Cl

Answer explanation

An ionic bond forms between a metal and a nonmetal. Among the choices, Ca and Cl are the only pair of a metal (Ca) and a nonmetal (Cl).

The Lewis symbol is for what group of elements?

• Noble Gases

• Alkali Metals

• Alkaline Earth Metals

• Halogens

Answer explanation

The Lewis symbol shows 7 dots corresponding to 7 valence electrons. Group 17 elements, also known as Halogens, have 7 valence electrons.

Tags

NGSS.HS-PS1-1

Which of the following is TRUE of metals?

• They tend to gain electrons and form positive ions.

• They tend to lose electrons and form negative ions.

• They tend to gain electrons and form negative ions.

• They tend to lose electrons and form positive ions.

Tags

NGSS.HS-PS1-2

The atomic property that refers to the energy required to remove an electron from an atom:

• atomic size

• mass number

• ionization energy

• atomic number

The halogen that has the biggest atom is:

• Ra

• At

• Ar

• Rn

Answer explanation

Among the choices, only Rn and Ar are noble gases. The trend in atomic radius for elements belonging to the same group is from Top to Bottom, atomic radius increases. Rn is in Period 7 while Ar is in Period 3, so Rn has the bigger radius.

Tags

NGSS.HS-PS1-1