Question

1. together, just four elements make up more than 95 percent of the body’s mass. these include a. calcium, magnesium, iron, and carbon b. oxygen, calcium, iron, and nitrogen c. sodium, chlorine, carbon, and hydrogen d. oxygen, carbon, hydrogen, and nitrogen 5. the smallest unit of an element that still retains the distinctive behavior of that element is an a. electron b. atom c. elemental particle d. isotope 6. the characteristic that gives an element its distinctive properties is its number of a. protons b. neutrons c. electrons d. atoms 7. on the periodic table of the elements, mercury (hg) has an atomic number of 80 and a mass number of 200.59. it has seven stable isotopes. the most abundant of these probably have 9. which of the following is a molecule, but not a compound? a. h₂o b. ²h c. h₂ d. h⁺ 10. a molecule of ammonia contains one atom of nitrogen and three atoms of hydrogen. these are linked with a. ionic bonds b. nonpolar covalent bonds c. polar covalent bonds d. hydrogen bonds 11. when an atom donates an electron to another atom, it becomes a. an ion b. an anion c. nonpolar d. all of the above 12. a substance formed of crystals of equal numbers of cations and anions held together by ionic bonds is called a(n) a. noble gas b. salt

Explanation:

1. Oxygen, carbon, hydrogen, and nitrogen make up more than 95 percent of the body's mass.
2. The smallest unit of an element that retains its characteristic behavior is an atom.
3. The number of protons gives an element its distinctive properties.
4. A molecule is a group of atoms held together by chemical bonds. A compound is a substance made up of two or more different types of elements. $H_2$ is a molecule but not a compound as it consists of only one type of element.
5. In ammonia ($NH_3$), nitrogen and hydrogen are linked by polar covalent bonds due to the electronegativity difference.
6. When an atom donates an electron, it becomes a positively - charged ion (cation). In general, an atom that gains or loses an electron is an ion.
7. A substance formed of crystals of equal numbers of cations and anions held together by ionic bonds is a salt.

Answer:

1. d. oxygen, carbon, hydrogen, and nitrogen
2. b. atom
3. a. protons
4. c. $H_2$
5. c. polar covalent bonds
6. a. an ion
7. b. salt