answers2e ch02
Mastering Concepts
2.1
1. Which chemical elements do organisms require in large amounts?
Carbon, oxygen, hydrogen, nitrogen, sulfur, and phosphorus are the chemical elements that organisms require in large amounts.
2. Where in an atom are protons, neutrons, and electrons located?
An atom’s protons and neutrons are in its nucleus. A cloud of electrons surrounds the nucleus.
3. What does an element’s atomic number indicate?
An atom’s atomic number indicates the number of protons in its nucleus.
4. What is the relationship between an atom’s mass number and an element’s atomic mass?
An atom’s mass number is the sum of protons and neutrons in its nucleus. The atomic mass is the average mass of all of the isotopes of that particular element.
5. How are different isotopes of the same element different from one another?
Isotopes of the same element differ in the number of the neutrons in their nuclei.
2.2
1. How are atoms, molecules, and compounds related?
Molecules and compounds are formed of atoms. Molecules are joined atoms, while compounds are molecules formed of two or more different elements.
2. How does the number of valence electrons determine an atom’s tendency to form bonds?
The number of valence electrons in the valence shell determines how many “vacancies” an atom has to fill before it is stable. If its valence shell is filled, it is chemically inert; if it has one or more vacancies it tends to be chemically reactive.
3. Explain how electronegativity differences between atoms result in nonpolar covalent bonds, polar covalent bonds, and ionic bonds.
The difference in electronegativity between atoms results in different kinds of bonds: nonpolar covalent bonds form between atoms that have similar electronegativity and share bond electrons equally; polar covalent bonds form between atoms that have different levels of electronegativity and share bond electrons unequally; ionic bonds form between pairs of atoms that have extremely different
2.1
1. Which chemical elements do organisms require in large amounts?
Carbon, oxygen, hydrogen, nitrogen, sulfur, and phosphorus are the chemical elements that organisms require in large amounts.
2. Where in an atom are protons, neutrons, and electrons located?
An atom’s protons and neutrons are in its nucleus. A cloud of electrons surrounds the nucleus.
3. What does an element’s atomic number indicate?
An atom’s atomic number indicates the number of protons in its nucleus.
4. What is the relationship between an atom’s mass number and an element’s atomic mass?
An atom’s mass number is the sum of protons and neutrons in its nucleus. The atomic mass is the average mass of all of the isotopes of that particular element.
5. How are different isotopes of the same element different from one another?
Isotopes of the same element differ in the number of the neutrons in their nuclei.
2.2
1. How are atoms, molecules, and compounds related?
Molecules and compounds are formed of atoms. Molecules are joined atoms, while compounds are molecules formed of two or more different elements.
2. How does the number of valence electrons determine an atom’s tendency to form bonds?
The number of valence electrons in the valence shell determines how many “vacancies” an atom has to fill before it is stable. If its valence shell is filled, it is chemically inert; if it has one or more vacancies it tends to be chemically reactive.
3. Explain how electronegativity differences between atoms result in nonpolar covalent bonds, polar covalent bonds, and ionic bonds.
The difference in electronegativity between atoms results in different kinds of bonds: nonpolar covalent bonds form between atoms that have similar electronegativity and share bond electrons equally; polar covalent bonds form between atoms that have different levels of electronegativity and share bond electrons unequally; ionic bonds form between pairs of atoms that have extremely different