A&P - Chapter 2: "The Building Blocks of Matter"

The Primary Elements in the Body (11 Total)

1. Oxygen (65%) 2. Carbon (18.5%) 3. Hydrogen (9.5%) 4. Nitrogen (3.2%) 5. Calcium (1.5%) 6. Phosphorus (1%) 7. Potassium (0.4%) 8. Sulfur (0.3%) 9. Sodium (0.2%) 10. Chlorine (0.2%) 11. Magnesium (0.1%)

Explain why CH4 is one of the most common molecules found in nature. Are the bonds between the atoms ionic or covalent?

A carbon atom has four electrons in its valence shell. According to the octet rule, it will readily participate in chemical reactions that result in its valence shell having eight electrons. Hydrogen, with one electron, will complete its valence shell with two. Electron sharing between an atom of carbon and four atoms of hydrogen meets the requirements of all atoms. The bonds are covalent because the electrons are shared: although hydrogen often participates in ionic bonds, carbon does not because it is highly unlikely to donate or accept four electrons.

An Electron Shell

A layer of electrons that encircle the nucleus at a distinct energy level. The atoms of the elements found in the human body have from one to five electron shells, and all electron shells hold eight electrons except the first shell, which can only hold two.

Valence Shell

An atom's outermost electron shell. If the valence shell is full, the atom is stable; meaning its electrons are unlikely to be pulled away from the nucleus by the electrical charge of other atoms. If the valence shell is not full, the atom is reactive; meaning it will tend to react with other atoms in ways that make the valence shell full.

Radioactive Isotope

An isotope whose nucleus readily decays, giving off subatomic particles and electromagnetic energy.

Anion

Atom with a negative charge.

Cation

Atom with a positive charge.

Ion

Atom with an overall positive or negative charge.

Magnesium is an important element in the human body, especially in bones. Magnesium's atomic number is 12. Is it stable or reactive? Why? If it were to react with another atom, would it be more likely to accept or to donate one or more electrons?

Magnesium's 12 electrons are distributed as follows: two in the first shell, eight in the second shell, and two in its valence shell. According to the octet rule, magnesium is unstable (reactive) because its valence shell has just two electrons. It is therefore likely to participate in chemical reactions in which it donates two electrons.

Polar Molecule

Molecule with regions that have opposite charges resulting from uneven numbers of electrons in the nuclei of the atoms participating in the covalent bond.

Isotope

One of the different forms of an element, distinguished from one another by different numbers of neutrons.

Oxygen, whose atomic number is eight, has three stable isotopes: 16O, 17O, and 18O. Explain what this means in terms of the number of protons and neutrons.

Oxygen has eight protons. In its most abundant stable form, it has eight neutrons, too, for a mass number of 16. In contrast, 17O has nine neutrons, and 18O has 10 neutrons.

Proton, Neutron, and Electron

The number of positively-charged protons and non-charged ("neutral") neutrons, gives mass to the atom, and the number of each in the nucleus of the atom determine the element.

Atomic Number

The number of protons in the nucleus of the atom, identifying the element.

Atom

The smallest quantity of an element that retains the unique properties of that element.

Matter

The substance of the universe; anything that occupies space and has mass.

An Element's Mass Number

The sum of the number of protons and neutrons in its nucleus.

Molecule

Two or more atoms covalently bonded together.

In a hurry one day, you merely rinse your lunch dishes with water. As you are drying your salad bowl, you notice that it still has an oily film. Why was the water alone not effective in cleaning the bowl?

Water is a polar molecule. It has a region of weakly positive charge and a region of weakly negative charge. These regions are attracted to ions as well as to other polar molecules. Oils are nonpolar, and are repelled by water.

Bond

Electrical force linking atoms.

Elements

A pure substance that is distinguished from all other matter by the fact that it cannot be created or broken down by ordinary chemical means.

Compound

A substance composed of two or more elements joined by chemical bonds.

The characteristic that gives an element its distinctive properties is its number of: A). protons B). neutrons C). electrons D). atoms

A.

When an atom donates an electron to another atom, it becomes: A). an ion B). an anion C). nonpolar D). all of the above

A.

Which of the following statements about chemical bonds is true? A). Covalent bonds are stronger than ionic bonds. B). Hydrogen bonds occur between two atoms of hydrogen. C). Bonding readily occurs between nonpolar and polar molecules. D). A molecule of water is unlikely to bond with an ion.

A.

Ionic Bond

Attraction between an anion and a cation.

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 C). electrolyte D). dipole

B.

Nitrogen has an atomic number of seven. How many electron shells does it likely have? A). one B). two C). three D). four

B.

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

B.

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

C.

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: A). about 80 neutrons each B). fewer than 80 neutrons each C). more than 80 neutrons each D). more electrons than neutrons

C.

Which of the following is a molecule, but not a compound? A). H2O B). 2H C). H2 D). H+

C.

Covalent Bond

Chemical bond in which two atoms share electrons, thereby completing their valence shells.

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

D.

Hydrogen Bond

Dipole-dipole bond in which a hydrogen atom covalently bonded to an electronegative atom is weakly attracted to a second electronegative atom.

Could two atoms of oxygen engage in ionic bonding? Why or why not?

Identical atoms have identical electronegativity and cannot form ionic bonds. Oxygen, for example, has six electrons in its valence shell. Neither donating nor accepting the valence shell electrons of the other will result in the oxygen atoms completing their valence shells. Two atoms of the same element always form covalent bonds.