BIOL 101- Ch.2

Partial charges occur when ...

(a) a covalent bond links atoms of two kinds. (b) atoms share electrons unequally.

Covalent bonds hold atoms together because they ...

(a) fill shells without giving atoms much charge. (b) bring electrons closer to protons.

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

Drag the terms on the left to the appropriate blanks on the right to complete the sentences. Terms may be used more than once.

1. When an electron absorbs the required amount of light energy, it moves from a lower electron shell to a higher electron shell, which is farther from the nucleus 2. When an electron loses a discrete amount of energy, it moves from a higher electron shell to a lower electron shell, which is closer to the nucleus.

Fluorine's atomic number is 9 and its atomic mass is 19. How many neutrons does fluorine have?

10

The innermost electron shell of an atom can hold up to _____ electrons.

2

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

2 electrons

What is the mass number of an ion with 105 electrons, 159 neutrons, and a +1 charge?

265

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

3 7-2-2=

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

An uncharged atom of boron has an atomic number of 5 and an atomic mass of 11. How many protons does boron have?

5

What is the atomic number of an atom that has 6 protons, 6 neutrons, and 6 electrons?

6

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.

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.

Which statement about relative potential energy of electrons is correct?

An electron in the 3 p orbital of the third electron shell has more potential energy than an electron in the 2 p orbital of the second electron shell.

What does the term electron orbital describe?

An electron orbital describes a three-dimensional space where an electron can be found 90% of the time

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

The brackets are indicating a(n) _____ bond.

Hydrogen

What can happen to an electron when sunlight hits it?

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

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 of these relationships is true of an uncharged atom?

The number of protons is equal to the number of electrons.

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

The valence shell needs 8 electrons.

Which of these refers to atoms with the same atomic number but different atomic masses?

These atoms are isotopes.

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

Which of the following lists some of the levels of biological organization from less complex to more complex?

atoms, molecules, cells, organs

What type of bond is joining the two hydrogen atoms?

covalent

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

double covalent

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

electrons in two orbitals.

The ammonia molecule in the diagram has the observed bond orientation because ...

electrons repel one another. N has four pairs of electrons in the valence shell. N has 7 protons in its nucleus.

A substance that cannot be broken down into other substances by ordinary chemical procedures is a(n) _____. See Concept 2.1

element

Compare the three atom diagrams. Which one shows the electron with the highest potential energy?

farther the electron, higher the potential energy

What determines the types of chemical reactions that an atom participates in?

he number of electrons in the outermost electron shell

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

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