MasteringBiology Chapter 2

An electrically neutral molecule has the formula C3H4O2N. If the carbon atoms form the usual number of bonds, how many covalent bonds will each hydrogen atom have with other atoms in the molecule?

1

To fill the valence shell, an electrically neutral, unbonded atom with atomic number 8 must add ...

2 electrons.

An atom's atomic number is 7. Its valence is most likely ...

3

This atom can form up to _____ single covalent bond(s).

4

In molecules, C, H, O, and N atoms usually make __, __, __, and __ bonds respectively.

4, 1, 2, 3

What happens when two atoms form a chemical bond?

A chemical bond forms when two atoms transfer or share outer electrons to complete their outer shells.

The ammonia molecule in the diagram has the observed bond orientation because ... N has 7 protons in its nucleus. N has four pairs of electrons in the valence shell. electrons repel one another. All of the above. None of the above.

All of the above.

Two C atoms form a double bond. Each C is bound to two H atoms. Which statement is true?

All the atoms lie in a plane.

Electrons are held in an atom by attraction to what particle or location?

Attraction to the positively charged protons in the nucleus

The atomic number of sulfur is 16. Sulfur combines with hydrogen by covalent bonding to form a compound, hydrogen sulfide. Based on the number of valence electrons in a sulfur atom, predict the molecular formula of the compound.

H2S

What can happen to an electron when sunlight hits it? Select all that apply.

It can move out to a higher electron shell. It can stay in its original shell.

Sort the subatomic particles according to their masses. Drag each subatomic particles into the correct bin.

MASS OF ~1 AMU: neutron, proton MASS OF ~1/2000 AMU: electron

Match each property to the appropriate subatomic particle. Drag each property into the correct bin.

PROTON: symbol p, +1 charge NEUTRON: symbol n, 0 charge ELECTRON: symbol e, -1 charge

By making two covalent bonds, an O atom (with 8 protons) fills its valence shell. Why does the atom's charge stay close to zero?

Shared electrons aren't always near oxygen.

Which answer helps to explain why carbon atoms tend to make 4 covalent bonds?

The valence shell needs 8 electrons.

Which statement about weak bonds is correct?

Weak bonds are transient and easily reversible.

An ionic bond involves _____.

an attraction between ions of opposite charge

Atoms with the same number of protons but with different electrical charges _____.

are different ions

Partial charges occur when ... (a) a covalent bond links atoms of two kinds. (b) atoms share electrons unequally. (c) two ions are close together. any of the above occur. both (a) and (b).

both (a) and (b).

What type of bond is joining the two hydrogen atoms?

covalent

Covalent bonds hold atoms together because they ... (a) fill shells without giving atoms much charge. (b) bring electrons closer to protons. (c) use forces between nuclei as well as forces between electrons. do all of the above. do both (a) and (b).

do both (a) and (b).

A(n) _____ bond joins these two oxygen atoms.

double covalent

In a double covalent bond, a carbon atom shares ...

electrons in two orbitals.

A substance that cannot be broken down into other substances by ordinary chemical procedures is a(n) _____.

element

When an electron loses a discrete amount of energy, it moves from a ________ electron shell to a ______ electron shell, which is _____________ the nucleus.

higher...lower...closer to

The brackets are indicating a(n) _____ bond.

hydrogen

What name is given to the bond between water molecules?

hydrogen

In salt, what is the nature of the bond between sodium and chlorine?

ionic

When an electron absorbs the required amount of light energy, it moves from a ________ electron shell to a __________ electron shell, which is _________________ the nucleus.

lower...higher...farther from

A(n) _____ refers to two or more atoms held together by covalent bonds.

molecule

Changing the number of _____ would change an atom into an atom of a different element.

protons in an atom

Without making or breaking bonds, the pictured molecule can change its shape because ...

rotation can occur around single bonds.

What type of bond joins the carbon atom to each of the hydrogen atoms?

single (nonpolar) covalent

Chemical equilibrium is reached when _____.

the forward and reverse reactions occur at the same rate so that the concentrations of reactants and products remain the same