UPCAT Science 8 Chemistry

acid

compound that gives off H+ ions in solution

acidic

describes a solution with a high concentration of H+ ions

anion

ions with a negative charge

anode

the electrode where electrons are lost (oxidized) in redox reactions

atmospheres

common units for measuring pressure

atom

the smallest object that retains properties of an element. Composed of electrons and a nucleus (containing protons and neutrons)

atomic number

number of protons in an element

Avogadro's number

number representing the number of molecules in (1) mole: 6.022 * 10 to the 23 power

base

substance which gives off hydroxide ions (OH-) in solution

basic

having the characteristics of a base

Bohr's atom

He made significant contributions to the atom. He understood the line spectra--the reason why only certain wavelengths are emitted when atoms jump down levels

buffer solutions

solutions that resist change in their pH, even when small amounts of acid or base are added

catalyst

substances that speed up a chemical process without actually changing the products of reactions

cathode

electrode where electrons have gained (reduction) in redox reactions

cations

ion with positive charge

central atom

in a Lewis structure, usually the atom that is the least electronegative

charge

describes an object's ability to repel or attract other objects. Protons have a positive ...while electrons have a negative... Like ...repel each other, while opposites attract.

chemical changes

processes or events that have altered the fundamental structure of something

chemical equation

an expression of a fundamental change in the chemical substance

colligative properties

properties of a solution that depend only on the number of particles dissolved in it, not the properties of the particles themselves. The main ones are boiling point elevation and freezing point depression.

combustion

when substances combine with oxygen and release energy

compound

two or more atoms joined together chemically, with covalent or ionic bonds

concentration

the amount of a substance in a specified space

conjugate acid

a substance which can lose H+ ion to form a base

conjugate base

a substance which can gain H+ ion to form an acid

covalent bonds

when two atoms share at least one pair of electrons

decay

change of an element into a different element, usually with some other particle(s) of energy emitted

density

mass per unit volume of a substance

dipole-dipole forces

intermolecular forces that exist between polar molecules. Active only when the molecules are close together. The strengths of intermolecular attractions increase when polarity increases

dispersion forces (London dispersion forces)

dispersion is an intermolecular attraction force that exists between all molecules. These forces are the result of the movement of electrons which cause slight polar moments. Generally very weak, when their molecular mass increases, so does their strength

dissociation

breaking down of a compound into its components to form ions from an ionic substance

double bond

when an atom is bonded to another atom by two sets of electron pairs

effusion

movement of gas molecules through a small opening

electrochemical cell

gives an electric current with a steady voltage as a result of an electron transfer reaction

electrodes

device that moves electrons into or out of a solution by conduction

electrolysis

changing the chemical structure of a compound using electrical energy

electromagnetic spectrum

complete range of wavelengths which light can have. These include infrared, ultraviolet and all other types of radiation as well as visible light

electrong

one of the parts of an atom having a negative charge. Indivisible particle with a charge of -1

electronegativity

measure of a substance's ability to attract electrons

electrostatic forces

forces between charged objects

element

substance consisting of only one type of atom

empirical formula

formula showing the simplest ratio of elements in a compound

endothermic

process that absorbs heat from its surroundings as the reaction proceeds

energy

ability to do work

enthalpy

change in heat at constant pressure

entropy

measure of the disorder of a system

equilibrium

when the reactants and products are in a constant ratio. The forward reaction and the reverse reactions occur at the same rate when a system is in this state

equilibrium constant

value that expresses how far the reaction proceeds before reaching equilibrium. A small number means that equilibrium is towards the reactants side while a large number means that the equilibrium is towards the product side

equilibrium expression

the expression giving the ratio between the products and reactants. It is equal to the concentration of each product raised to its coefficient in a balanced chemical equation and multiplied together, divided by the concentration of the product of reactants to the power of their coefficients

equivalence point

occurs when the moles of acid equal the moles of base in a solution

exothermic

process that gives off heat to the environment

frequency

number of events in a given unit of time. When describing a moving wave, means the number of peaks which would pass a stationary point in a given amount of time

Geiger counter

instrument that measures radiation output

Gibb's free energy

the energy of a system that is available to do work at a constant temperature and pressure

Graham's law

the rate of diffusion of a gas is inversely proportional to the square root of its molar mass

half life

the amount of time it takes for half an initial amount to disintegrate

Heisenberg uncertainty principle

the principle states that it is not possible to know a particle's location and momentum precisely at any time

hydrogen bonding

strong type of intermolecular dipole-dipole attraction. Occurs between hydrogen and F, O or N

hydrolysis

the reactions of cations with water to produce a weak base or of anions to produce a weak acid

ideal gas law

intermolecular forces

forces between molecules

intramolecular forces

forces within molecules. Forces caused by the attraction and repulsion of charged particles

ion

removing or adding electrons to an atom creates an ... (a charged object very similar to an attom)

ionic bond

when two oppositely charged atoms share at least one pair of electrons but the electrons spend more time near one of the atoms than the other

ionization energy

energy required to remove an electron from a specific atom

isotopes

elements with the same number of protons but have different numbers of neutrons, and thus different masses

Kelvin

The SI unit of temperature. It is temperature in degrees Celsius plus 273.15

kinetic energy

energy an object has because of its mass and velocity. Objects that are not moving do not have this.

Le Chatlier's Principle

states that a system at equilibrium will oppose any change in the equilibrium conditions

Lewis structures

a way of representing molecular structures based on valence electrons

limiting reagent

the reactant that will be exhausted first

mass number

the number of protons and neutrons in an atom

mixture

composed of two or more substances, but each keeps its original properties

molality

the number of moles of solute (the material dissolved) per kilogram of solvent (what the solute is dissolved in)

molar

a term expressing molarity, the number of moles of solute per liters of solution

molarity

the number of moles of solute (the material dissolved) per liter of solution. used to express the concentration of a solution

mole

a collection of 6.022 * 10 to the 23 power number of objects. Usually used to mean molecules

molecular formula

shows the number of atoms of each element present in a molecule

molecular geometry (VSEPR)

shape of a molecule, based on the relative position of the atoms

molecular mass

the combined mass (as given on the periodic table) of all the elements in a compound

molecule

two or more atoms chemically combined

mole fraction

the number of moles of a particular substance expressed as a fraction of the total number of moles

neutral

an object that does not have a positive or negative charge

neutron

a particle found in the nucleus of an atom. It is almost identical in mass to a proton, but carries no electrical charge

nm

abbreviation for nanometers. A nanometer is equal to 10 to the -9 power meters

nucleus

the central part of an atom that contains the protons and neutrons. Plural\=nuclei

octet

In Lewis structures, the goal is to make almost all atoms have this structure. This means they will have access to (8) electrons regularly, even if they do have to share some of them

orbitals

an energy state in the atomic model which describes where an element will likely be

oxidation number

a number assigned to each atom to help keep track of the electrons during a redox-reaction

oxidation-reduction-reaction

a reactions involving the transfer of electrons

parent isotopes

an element that undergoes nuclear decay

partial pressure

the pressure exerted by a certain gas in a mixture

particle

small portion of matter

percent composition

expresses the mass ratio between different elements in a compound

periodic table

grouping of the known elements by their number of protons. There are many other trends such as size of elements and electronegativity that are easily expressed in terms of the periodic table

pH

measures the acidity of a solution. It is the negative log of the concentration of the hydrogen ions in a substance

photon

massless packet of energy, which behaves like both a wave and a particle

physical property

a property that can be measured without changing the chemical composition of a substance

Planck

What is h?

Planck

He contributed to the understanding of the