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acid - 27
To a chemist, acids are substances that dissociate in water, releasing hydrogen ions (H+).
Def: Molecules tending to raise the hydrogen ion concentration in a solution and to lower its pH numberically. 27
Atom - 18
The atomic theory states that elements consist of tiny particles called atoms.
Def: Smallest particle of an element that displays the properties of the elements. 18
atomic mass - 18
The atomic mass of an atom is dependent upon the presence of three types of sub-atomic particles: neutrons, which have no electrical charge; protons, which have a positive charge; electrons, which have a negative charge.
Def: Mass of an atom equal to the number of protons plus the number of neutrons within the nucleus.
atomic number - 19
Def: Number of protons within the nucleus of an atom. -19
Atomic Symbol - 18
Because each element consists of only one kind of atom, the same name is given to an element and its atoms. The name is represented by one or two letters, called atomic symbol.
Def: One or two letters that represent the name of an element - e.g., H stands for a hydrogen atom, and Na stands for sodium atom. 18
base - 27
To a chemist, bases are substances that either take up hydrogen ions (H+) or release hydroxide ions (OH-).
Def: Molecules tending to lower the hydrogen ion concentration in a solution and raise the pH numberically, 27
buffer - 28
A buffer is a chemical or a combination of chemicals that keeps pH within normal limits.
Def: Substance or group of substances that tend to resist pH changes of a solution, thus stabilizing its relative acidity and basicity. 28
Compound - 21
When a molecule contains atoms of more than one element, it can be called a compound.
Def: Substance having two or more different elements united chemically in a fixed ration. 21
Covalent Bond - 22
A covalent bond results when two atoms share electrons in order to have a completed outer shell.
Def: Chemical bond in which atoms share one pair of electrons. -22
electron - 18
The atomic mass of an atom is dependent upon the presence of three types of subatomic particles: neutrons, which have no electrical charge; protons, which have a positive charge; and electrons, which have a negative charge.
Def: Negative subatomic particle, moving about in an energy level around the nucleus of an atom. -18
Atoms differ in their electronegativity -- that is, their affinity for electrons in a covalent bond.
Def: Ability of an atom to attract electrons toward itself in a chemical bond. 24
electron shell -20
Each energy level contains a certain number of electrons. The energy levels (electron shells) are drawn as concentric rings about the nucleus.
Def: Concentric energy levels in which electrons orbit. 20
element - 18
An element is a substance that cannot be broken down into another substance by ordinary chemical means.
Def: Substance that cannot be broken down into substances with different properties; composed of only one type of atom. 18
hydrogen (H) bond -24
This attraction is called a hydrogen (H) bond, and each water molecule can engage in as many as four H bonds
Def: Weak bond that arises between a slightly positive hydrogen atom of one molecule and a slightly negative atom of another molecule or between parts of the same molecule. 24
Molecules that are attracted to water are said to be hydrophilic (hydro, water, phil, love).
Def: Type of molecule that does not interact with water because it is nonpolar.
hydrogen ion (H+) page 27
Dissociation of water molecules produces and equal number of hydrogen ions (H+) and Hydroxide ions (OH-)
Def: Hydrogen atom that has lost its electron and therefore bears a positive charge (H+). 27
hydrophobic - 25
Non-ionized and nonpolar molecules that are not attracted to water are said to be hydrophobic (hydro, water; phob, fear).
Def: Type of molecule that does NOT interact with water because it is nonpolar. 25,33
hydroxide -ion (OH-) page 27
Dissociation of water molecules produces and equal number of hydrogen ions (H+) and hydroxide ions (OH-).
Def: One of two ions that results when a water molecule dissociates; it has gained an electron, and therefore bears a negative charge (OH-). 27
ion - 22
This electron transfer causes these atoms to become ions, or charged atoms.
Def: Charged particle that carries a negative or positive charge. 22
ionic bond - 22
An ionic bond forms when two atoms are held together by the attraction between opposite charges.
Def: Chemical bond in which ions are attracted to one another by opposite charges. 22
isotope - 19
Isotopes are atoms of the same element that differ in the number of neutrons.
Def: Atom of the same element having the same atomic number but a different mass number due to the number of neutrons. 19
Matter refers to anything that takes up space and has mass.
Def: Anything that takes up space and has mass. 18
molecule - 21
A group of atoms bonded together is called a molecule.
Def: Union of two or more atoms of the same element; also, the smallest part of a compound that retains the properties of the compound. 21
neutron - 18
Def: Neutral subatomic particle, located in the nucleus and assigned one atomic mass unit. 18
Protons and neutrons are located within the center of an atom, which is called its nucleus, while electrons move about the nucleus.
Def: 1.Center of an atom, in which protons and neutrons are found;
2. Membrane-bound organelle within a eukaryotic cell that contains chromosomes and controls the structure and function of the cell.
octet rule - 21
If an atom has two or more shells, the outer shell is most stable when it has eight electrons; this is called the octet rule.
Def: States that an atom other than hydrogen tends to form bonds until it has eight electrons in it outer shell; an atom that already has eight electrons in its outer shell does not react and is inert. 21
pH - 28
pH is a mathematical way of indicating the number of hydrogen ions in a solution.
pH is defined as the negative log of the hydrogen ion concentration (H+). A log is the power to wyhich 10 must be raised to produce a given number.
Def: Hydrogen ion concentration. 28
pH scale -28
The pH scale is used to indicate the acidity or basicity (alkalinity) of a solution.
Def: Measurement scale for hydrogen ion concentration. 28
This causes the bond to become polar, meaning that the atoms on either side of the bond are partially charged, even though the overall molecule itself bears no net charge.
Def: In chemistry, bond in which the sharing of electrons between atoms is unequal. 24
product - 23
The reactants (molecules that participate in the reaction) are shown on the left of the arrow, and the products (molecules formed by the reaction) are shown on the right.
Def: Substance that forms as a result of a reaction. 23
proton - 18
Te atomic mass of an atom is dependent upon the presence of three types of subatomic particles: neutrons, which have no electrical charge; protons, which have a positive charge; and electrons which have a negative charge.
Def: Positive subatomic particle located in the nucleus and assigned one atomic mass unit. 18
The reactant (molecules that particpate in the reaction) are shown on the left of the arrow, and the products (molecules formed by the reaction) are shown on the right.
Def: Substance that participates in a reaction. 23
salt - 22
Ionic compounds are often found in salts.
Def: Compound produced by a reaction between an acid and a base. 22
tracer - 20
This means that you can put a small amount of radioactive isotope in a sample and it becomes a tracer by which to detect molecular changes because it behaves like the stable isotope.
Def: Substance having an attached radioactive isotope that allows a researcher to track its whereabouts in a biological system. 20
valence shell - 21
The number of electrons in an atom's outer shell, called the valence shell, determines its chemical reactivity.
Def: Outer shell of an atom.