Chapter 2 Notes Section 2 1 Atoms The smallest unit of a chemical element NUCLEUS The centrally located positive part of an atom containing the protons and neutrons ELECTRONS The negative particles that surround the nucleus PROTONS The positive charged subatomic particle in a nucleus NEUTRONS A particle of matter with no electrical charge that makes up part of the nucleus MASS A measure of the quantity of matter present Dalton standard unit of measurement used to measure the mass of a particle 1 dalton Da 1 7 x 10 24 grams ELEMENT A pure substance that contains only one kind of atom ATOMIC NUMBER The number of protons an atom contains MASS NUMBER The total number of protons and neutrons in an atom s nucleus ISOTOPE A chemical that has the same number of protons but differ in number of neutrons ATOMIC WEIGHT ATOMIC MASS The average mass number of a sample of atom s from a given element RADIOISOTOPE A radioactive isotope of an element that is unstable and spontaneously gives off energy in the form of alpha beta or gamma radiation from the nucleus MOLECULES A chemical substance made up of two or more atoms joined by covalent bonds or ionic attractions ORBITAL A region in space surrounding the atomic nucleus in which an election is most likely to be found ELECTRON SHELLS ENERGY LEVELS The region surrounding the atomic nucleus at a fixed energy level in which electrons orbit Valance shell outermost shell Reactive atoms can attain stability either by sharing electrons with other atoms or by losing or gaining one or more electrons Section 2 2 CHEMICAL BOND An attractive force that links two atoms together in a molecule COVALENT BOND Forms when two atoms attain stable electron numbers in their outermost shells by sharing one or more pairs of electrons COMPOUND A pure substance made up of two or more different elements bonded together in a fixed ratio MOLECULAR WEIGHT RELATIVE MOLECULAR MASS The sum of the atomic weights of all atoms in a molecule covalent bonds are VERY strong ELECTRONEGATIVITY The attraction force that an atomic nucleus exerts on electrons in a covalent bond depends on how many charges and the distance b w the nucleus and electrons in valence shell NONPOLAR COVALENT BOND The bond formed when two atoms that are close together in electronegativity share electrons equally POLAR COVALENT BOND A bond in which the electrons are drawn to one nucleus more than the other resulting in an unequal distribution of charge POLAR A molecule with separate and opposite electric charges at two ends or poles ION An electrically charged particle that forms when an atom gains or loses one or more electrons CATION A positively charged ion ANION A negatively charged ion COMPLEX IONS Groups of covalently bonded atoms that carry an electric charge IONIC ATTRACTIONS Bonds formed as a result of the electrical attraction between ions bearing opposite charges HYDROGEN BOND A weak bond formed by the attraction of a slight positive charged hydrogen atom and a slightly negative charged oxygen nitrogen atom HYDROPHILIC water loving HYDROPHOBIC water hating HYDROCARBON MOLECULES A compound containing only carbon and hydrogen atoms VAN DER WAALS FORCES Very weak attractions between atoms resulting from the interaction of the electrons of one atom with the nucleus of another Section 2 3 CHEMICAL REACTION Occurs when moving atoms collide with sufficient energy to combine or to change their bonding partners REACTANT A chemical substance that enters into a chemical reaction with another substance PRODUCT The molecule that results from the completion of a chemical reaction ENERGY The capacity to do work or the capacity for change Section 2 4 SPECIFIC HEAT The amount of heat energy required to raise the temperature of 1 gram of a substance by 1 degree Celsius HEAT OF VAPORIZATION The energy that must be supplied to convert a molecule from a liquid to a gas at its boiling point COHESION The capacity of water molecules to resist coming apart from one another when placed under tension SOLUTION A liquid and its dissolved solutes SOLUTE A substance that is dissolved in a liquid to form a solution SOLVENT The liquid in which a substance is dissolved to form a solution MOLE The amount of a substance numerically equal to the molecular weight AVOGADRO S NUMBER The constant number of molecules in a mole ACID Substances that release H BASE Substances that accept H BUFFER A mixture of a weak acid and its corresponding base or a weak base and its corresponding acid