chapter 2

Ion

an atom or molecule that has either lost or gained electrons Losing an electron results in a net positive charge. Gaining an electron results in a net negative charge.

Small amounts of radiation

can be used to image organs and tissues.

Nonpolar covalent bond

equal sharing of electrons between atoms

Calorie

the amount of heat energy needed to raise the temperature of 1 g of water 1°C High heat capacity - water holds onto heat

Electronegativity

the attraction of an atom for the electrons in a covalent bond In H2O, the larger oxygen atom is more electronegative than the hydrogen atoms. O atom is slightly negative (δ-, "delta minus") H atoms are slightly positive (δ+, "delta plus")

Adhesion

water molecules stick to other polar molecules

Compound

two or more different elements bonded together H2O

Polar covalent bond

- unequal sharing of electrons

Buffer

A buffer resists changes in pH. Buffers take up excess hydrogen ions (H+) or hydroxide ions (OH-). Blood and many other body fluids are buffered so the pH stays within a narrow range. Ecosystems are also buffered.

The pH scale ranges from 0 to 14.

A pH of 7 represents a neutral state. Hydrogen ion concentration [H+] equals hydroxide ion concentration [OH-] A pH below 7 is acidic. [H+] is greater than [OH-] A pH above 7 is basic. [OH-] is greater than [H+]

Atomic number

All atoms of an element have the same number of protons. Also tells you the number of electrons

Six elements of life:

Carbon - C Hydrogen - H Nitrogen - N Oxygen - O Phosphorus - P Sulfur - S

Mass Number

Depends on the number of protons and neutrons Electron mass is considered zero.

Chemical reactions

Electron exchanges between atoms create chemical reactions. Reactants participate in the reaction. Products are formed by the reaction.

Acids

Excess hydrogen ions Substances that dissociate in water, releasing hydrogen ions (H+)

Bases

Excess hydroxide ions Substances that either take up hydrogen ions (H+) or release hydroxide ions (OH-)

An atom's electron shells can be modeled.

For elements up to 20 (calcium) Each lower level fills before the next higher level. The innermost shell can contain 2 electrons. Each additional shell can contain 8 electrons.

Water molecules stick together and to other materials

Hydrogen bonding accounts for most of the properties of water that make life possible. Responsible for the freezing and boiling points of water

Both frozen and liquid water help organisms maintain a normal temperature

Hydrogen bonds help water absorb heat without a great change in temperature.

Electrons

Negatively charged particles in electron shells

harmful effects of acid rain

Normally, rainwater has a pH of about 5.6. Air pollution, particularly from burning fossil fuels, acidifies rainwater. Leaches toxic aluminum and creates methyl mercury in lakes Destroys leaves, stopping photosynthesis and making trees susceptible to disease Increases respiratory disease and erodes buildings and monuments

Protons

Positively charged particles in the nucleus

Elements can be arranged in a periodic table.

Row tells how many shells an atom has Column tells how many electrons in its outer shell

Bond notation

Single covalent bonds are written as H-H. Double covalent bonds are written as O=O. Triple covalent bonds are written as N≡N.

Atom

Smallest unit of an element Every element has a name and an atomic symbol.

A solution contains

Solute - dissolved solid Solvent - liquid Water's hydrogen bonds help it dissolve other polar molecules.

Element

Substance that cannot be broken down by chemical means into a simpler substance

Neutrons

Uncharged particles in the nucleus

High levels of radiation

Will damage DNA and kill cells Can be used to sterilize Can target rapidly growing cells (radiotherapy)

molecule

the smallest part of a compound that still has the properties of that compound

Isotopes

Atoms of a single element that differ in their number of neutrons Have the same number of protons, but different mass numbers

Octet rule

Atoms will give up, accept, or share electrons in order to have 8 electrons in the outer shell.

Atomic mass

Average mass of all an element's isotopes

Water has a high heat of vaporization because so many hydrogen bonds must be broken.

Efficient way to release body heat Water is more dense at 4°C than it is at 0°. When water freezes, its crystal lattice expands. Ice floats on water.

ionic bonds

Ions with opposite charges attract

valence shell

The number of electrons in the valence shell determines chemical reactivity.

Hydrophilic

molecules attract water. Ionic salts, ionized or polar molecules

hydrophobic

molecules cannot attract water. Nonionized and nonpolar molecules

Hydrogen bond

polarity of water molecules causes the hydrogen atoms in one molecule to be attracted to the oxygen atoms in other water molecules Easily broken Often represented by a dotted line

cohesion

water molecules stick together

Covalent bond

when two atoms do not have completely full outer shells, they may share electrons so that each has a full outer shell Example: Hydrogen (H2)