Question 1

If an atom has a charge of +1,which of the following must be true?

Accepted Answer

An atom with a charge of +1 means it has lost one negatively charged electron, leaving it with one less negatively charged particle than positively charged particles. Therefore, it has one more proton than electrons.

Question 2

What holds electrons in a covalent bond?

Accepted Answer

In a covalent bond, electrons are held together by the electrostatic attraction between the negative charges of the electrons and the positive charges of both nuclei. The atoms do not become smaller or more compact, and potential energy does not increase due to electrical repulsion. While electron pairing does play a role in covalent bonding, it is not the primary factor holding the electrons together.

Question 3

When are atoms most stable?

Accepted Answer

When all of the electron orbitals in the valence shell are filled, the atom is most stable because it has achieved a full valence shell, which is the most energetically favorable configuration for the atom. This is known as the octet rule, which states that atoms tend to gain, lose, or share electrons in order to achieve a full valence shell with eight electrons (or two electrons for hydrogen and helium).

Question 4

You need to write down information about a molecule,but need to indicate only which atoms it contains and how many of each.Which representation would work best?

Accepted Answer

The molecular formula provides a precise representation of the atoms present in a molecule and the number of atoms of each element. It is the most concise and simplest way to represent a molecule. The other options (B, C, D) show the arrangement of atoms in a molecule, providing more detailed information than necessary in this case.

Question 5

If you change the number of neutrons in an atom,you create _____.

Accepted Answer

Changing the number of neutrons in an atom creates an isotope. Isotopes are atoms of the same element that have different numbers of neutrons in the nucleus.

Question 6

You need to write down information about a molecule that gives the most accurate picture of the relative sizes of the atoms involved and their relationship in space.Which representation would work best?

Accepted Answer

The space-filling model would give the most accurate picture of the relative sizes of the atoms and their relationship in space. This is because it shows the atoms as spheres that are scaled to accurately represent their relative sizes and how they are positioned in 3D space. The other choices (molecular formula, structural formula, and ball-and-stick model) may provide some information about the arrangement of the atoms, but they do not accurately represent their relative sizes or their relationship in space.

Question 7

You isolate a molecule and determine it is nonpolar.Based on this property,the molecule is largely composed of the elements _____.

Accepted Answer

Nonpolar molecules are largely composed of nonpolar covalent bonds between atoms of similar electronegativity. Carbon and hydrogen have similar electronegativities and form nonpolar covalent bonds, making them a likely choice for a nonpolar molecule. Oxygen and nitrogen are more electronegative than carbon and have polar covalent bonds when paired with carbon, making them less likely to contribute to a nonpolar molecule.

Question 8

An atom has six electrons in its valence shell.How many single covalent bonds would you expect it to form in most circumstances?

Accepted Answer

An atom with six electrons in its valence shell, like oxygen, typically forms two single covalent bonds to achieve a stable octet configuration.

Question 9

Which of the following is the best description of an atom's physical structure?

Accepted Answer

The current understanding of an atom's physical structure is that it consists of a nucleus at the center, which contains protons and neutrons, and electrons orbiting around the nucleus. However, the majority of an atom is actually empty space, with the electrons existing in a cloud-like region around the nucleus. This means that atoms can be described as little bubbles of space, with the mass concentrated at the center of the bubble in the form of the nucleus. Choice A is incorrect because atoms are not solid masses of material. Choice B is incorrect because while the particles within an atom are arranged in a regular pattern, they are not necessarily equidistant from each other. Choice D is incorrect because the mass is not concentrated on the outside surface of the bubble.

Question 10

Nitrogen (N)normally forms only three covalent bonds because it has a valence of five.However,ammonium has four covalent bonds,each to a different hydrogen (H)atom (H has a valence of one).Make a sketch of this molecule.Count the number of electrons in your sketch.Compare this number to the number of valence electrons in one N and four H's.What do you predict to be the charge on this molecule?

Accepted Answer

Ammonium (NH4+) has a total of 9 valence electrons (5 from N and 1 from each of the 4 H atoms). However, it forms 4 covalent bonds, using 8 electrons, and has one extra proton, resulting in a +1 charge.

Question 11

An atom has four electrons in its valence shell.What types of covalent bonds is it capable of forming?

Accepted Answer

An atom with four electrons in its valence shell can form single, double, or triple covalent bonds by sharing electrons with other atoms to achieve a stable octet configuration.

Question 12

Can the atomic mass of an element change?

Accepted Answer

The atomic mass of an element can change if there is a change in the number of neutrons, which is the basis for isotopes. Isotopes are atoms of the same element with different numbers of neutrons, resulting in different atomic masses but not forming a different element. Adding or losing electrons or protons can change the ionization state of an atom, but it does not change the atomic mass or result in a different element.

Question 13

Elements found on the left side of the periodic table contain outer shells that are _____;these elements tend to form _____ in solution.

Accepted Answer

Elements on the left side of the periodic table have fewer electrons in their outermost shell, making their outer shells almost empty. As a result, they tend to lose electrons and form cations in solution.

Question 14

The structural formula for a certain molecule includes a group symbolized -O.The dash next to the oxygen atom means that a single bond exists to another atom,such as a carbon.Based on the valence of oxygen and the number of bonds it normally forms,what is the charge on the oxygen atom in this case?

Accepted Answer

Oxygen typically has 6 valence electrons and forms 2 bonds, resulting in a charge of -2. Since it is only forming one bond in this molecule, it would have a charge of -1 to balance out the bond.

Question 15

How many electrons are involved in a single covalent bond?

Accepted Answer

In a single covalent bond, two electrons are shared between two atoms, with each atom providing one electron to the bond. Therefore, the correct answer is B) two.

Question 16

When the atoms involved in a covalent bond have the same electronegativity,what type of bond results?

Accepted Answer

When the atoms involved in a covalent bond have the same electronegativity, the electrons are shared equally resulting in a nonpolar covalent bond. This is because there is no polarity difference between the atoms to cause the electrons to be attracted to one atom more than the other.

Question 17

Which of the following is true of carbon?

Accepted Answer

Carbon can form both polar (such as with oxygen) and nonpolar (such as with other carbons) covalent bonds. It is not highly electronegative, and it can form up to four covalent bonds with other elements.

Question 18

How many electrons are involved in a double covalent bond?

Accepted Answer

A double covalent bond involves the sharing of two pairs of electrons, which totals four electrons.

Question 19

Which of the following molecules is polar?

Accepted Answer

The answer of Which of the following molecules is polar?
...

Question 20

Silicon's atomic number is 14;in the periodic table it is directly beneath carbon.Silicon is abundant in the Earth's crust,yet,unlike C,N,O,and H,silicon is not a common element in organisms.What about the atomic structure of silicon probably accounts for this?

Accepted Answer

Silicon atoms are larger than carbon atoms, which makes Si-Si bonds less stable and less favorable for forming long chains like carbon does.

Quiz 2: Water and Carbon: the Chemical Basis of Life