Chemical Level (235 #2) Flashcards
solid
compact and have a definite shape and volume
liquids
definite volume and assume the shape of their container
gas
neither a definite shape nor volume
chemical elements
a substance that cannot be split into a simpler substance by ordinary chemical means. Scientists now recognize 117 elements. Of these, 92 occur naturally on Earth.
4 major elements
make up 96% of the body’s mass - O, C, H, N
8 lesser elements
make up about 3.6% of the body’s mass - Ca, Fe, K, Ph, Mg, Na, Cl, S
subatomic particles
The dense central core of an atom is its nucleus. Within the nucleus are positively charged protons () and uncharged (neutral) neutrons (). The tiny, negatively charged electrons () move about in a large space surrounding the nucleus. They do not follow a fixed path or orbit but instead form a negatively charged “cloud” that envelops the nucleus
atomic number
The number of protons in the nucleus of an atom
mass number
the sum of its protons and neutrons
Isotopes
atoms of an element that have different numbers of neutrons and therefore different mass numbers
half‐life
he time required for half of the radioactive atoms in a sample of that isotope to decay into a more stable form.
atomic mass
(also called the atomic weight) of an element is the average mass of all its naturally occurring isotopes. Typically, the atomic mass of an element is close to the mass number of its most abundant isotope.
compound
a substance that contains atoms of two or more different elements
molecule
When two or more atoms share electrons
free radical
an atom or group of atoms with an unpaired electron in the outermost shell. Having an unpaired electron makes a free radical unstable, highly reactive, and destructive to nearby molecules. Free radicals become stable by either giving up their unpaired electron to, or taking on an electron from, another molecule - may break apart important body molecules.
antioxidants
substances that inactivate oxygen‐derived free radicals—is thought to slow the pace of damage caused by free radicals. Important dietary antioxidants include selenium, zinc, beta‐carotene, and vitamins C and E. Red, blue, or purple fruits and vegetables contain high levels of antioxidants.
ionic bond
The force of attraction that holds together ions with opposite charges
cation
positively charged ion
anion
negatively charged ion
electrolyte
An ionic compound that breaks apart into positive and negative ions in solution. Most ions in the body are dissolved in body fluids as electrolytes, so named because their solutions can conduct an electric current.
covalent bond
two or more atoms share electrons rather than gaining or losing them - a single (─), double (═), or triple (≡) covalent bond.
nonpolar covalent bond
two atoms share the electrons equally—one atom does not attract the shared electrons more strongly than the other atom
polar covalent bond
the sharing of electrons between two atoms is unequal—the nucleus of one atom attracts the shared electrons more strongly than the nucleus of the other atom. When polar covalent bonds form, the resulting molecule has a partial negative charge near the atom that attracts electrons more strongly. This atom has greater electronegativity, the power to attract electrons to itself. At least one other atom in the molecule then will have a partial positive charge.
hydrogen bond
when a hydrogen atom with a partial positive charge (δ+) attracts the partial negative charge (δ−) of neighboring electronegative atoms, most often larger oxygen or nitrogen atoms. Thus, hydrogen bonds result from attraction of oppositely charged parts of molecules rather than from sharing of electrons as in covalent bonds, or the loss or gain of electrons as in ionic bonds. Hydrogen bonds are weak compared to ionic and covalent bonds. Thus, they cannot bind atoms into molecules. However, hydrogen bonds do establish important links between molecules or between different parts of a large molecule, such as a protein or nucleic acid
surface tension
a measure of the difficulty of stretching or breaking the surface of a liquid
chemical reaction
when new bonds form or old bonds break between atoms
Energy
the capacity to do work
potential energy
energy stored by matter due to its position
kinetic energy
energy associated with matter in motion
law of conservation of energy
The total amount of energy present at the beginning and end of a chemical reaction is the same. Although energy can be neither created nor destroyed, it may be converted from one form to another.
Exergonic reactions
release more energy than they absorb
endergonic reactions
absorb more energy than they release
activation energy
The collision energy needed to break the chemical bonds of the reactants - This initial energy “investment” is needed to start a reaction. The reactants must absorb enough energy for their chemical bonds to become unstable and their valence electrons to form new combinations.
Concentration
The more particles of matter present in a confined space, the greater the chance that they will collide (think of people crowding into a subway car at rush hour). The concentration of particles increases when more are added to a given space or when the pressure on the space increases, which forces the particles closer together so that they collide more often.
Temperature
As temperature rises, particles of matter move about more rapidly. Thus, the higher the temperature of matter, the more forcefully particles will collide, and the greater the chance that a collision will produce a reaction.
Catalysts
hemical compounds that speed up chemical reactions by lowering the activation energy needed for a reaction to occur - enzymes. A catalyst does not alter the difference in potential energy between the reactants and the products. Rather, it lowers the amount of energy needed to start the reaction
