ATI TEAS 7 Introduction to Chemistry

atom is the basic unit of matter. They are also known as elements number of protons in an atom determines its identity (which element it is). atomic number mass number is determined by adding the number of protons and the number of neutrons. charge of an atom is determined by the numbers of protons and electrons. Isotopes atoms of the same element that have different numbers of neutrons and, therefore, different masses. Electron negative charge Proton positive charge Neutron neutral charge valance electrons number of unpaired electrons in the outermost shell 2 electrons are in the 1st shell 8 electrons are in the 2nd shell 18 electrons are in the 3rd shell full shell Electrons are located in an atom's electron cloud, divided into shells. Atoms are constantly seeking to gain, share, or give up electron in order to have a full shell. column or group have the same number of valence electrons in their outermost shell, there are exceptions Transition metals have 2 valence electrons (columns 3-12) atoms in columns 13-18 have the number of valence electrons equal to the column number minus 10. noble gas have 8 valence electrons and a full outermost shell. Exception: Helium (also noble gas) only has 2 valance electrons, its full. Cohesion is the tendency of particles of the same kind to stick to each other. States of matter energy A solid has the lowest amount of energy because its particles are packed close together. Liquids have more energy than a solid, and gases have more energy than solids or liquids because the cohesive forces are very weak. Matter can change phases if it either absorbs or releases enough energy. Sublimation phase change from solid directly to gas Deposition phase change from gas directly to solid When does a substance experience an increase or decrease in temperature? Only when it is entirely in one state of matter. While a substance changes states its temperature remains constant. Any energy that is absorbed or released is used to change the way in which the particles interact with one another. Properties of matter there are physical and chemical properties Physical properties categories intensive and extensive properties Intensive properties do not depend on the amount of matter present, such as color or density. Extensive properties do depend on the amount of a sample present, such as mass and volume. Water is what type of molecule? is considered a polar molecule, a molecule where one end is slightly negative and the other end is slightly positive. adhesiveness is the attraction of water to other substances. Cohesiveness is the attraction of water to itself, and adhesiveness is the attraction of water to other substances. Diffusion is the tendency of molecules and ions to move toward areas of lower concentrations until a substance is uniform. Osmosis is the diffusion of water and the movement of molecules from an area of high concentration to an area of lower concentration. octet rule any atom that does not have a stable electron configuration of eight valence electrons will lose, gain, or share electrons to become stable. Exceptions are hydrogen and helium since their outer layer is full with 2 electrons. Periodic table row Elements have the number of energy levels equivalent to the row they are in. Ionic bonds are formed when electrons are transferred from a metal atom to a nonmetal atom. anion it has a net negative charge since it gains negatively charged particles, electrons. cation when an ion loses electrons, it has a net positive charge since the newly formed ion will have more protons than electrons. Covalent bonds are formed when two atoms share electrons. When two atoms need to share more than one pair of electrons, multiple bonds form. If two pairs are shared, a double bond forms. If three pairs are shared, a triple bond forms. nonpolar covalent bond if electrons are shared equally polar covalent bond if electrons are shared unequally Lewis structures are diagrams of atoms to represent bonding. Valence electrons and lone-pair electrons, or electrons not involved in bonding, are represented with dots while bonding patterns are represented with lines. mixture is when elements and compounds are physically, but not chemically, combined. homogeneous mixture is when substances mix evenly and it is impossible to see individual components. heterogeneous mixture is when the substances mix unevenly and it is possible to see individual components. solution is a type of homogeneous mixture that is formed when a solute dissolves in a solvent. unsaturated solution solution has the ability to dissolve more solute saturated solution has already reached the limit of solute it can dissolve. concentration of a solution is the amount of a substance in a given amount of solution. The law of conservation of mass states that matter cannot be created or destroyed, but it can change forms. Chemical reactions occur when reactants combine, break apart, or rearrange to form products. Chemical equations represent chemical reactions using formulas and symbols. They must be balanced to obey the law of conservation of mass to ensure that all atoms at the beginning of the reaction in the reactants are accounted for at the end in the products. Chemical reactions classifications classified as synthesis, decomposition, single-replacement, double-replacement, or combustion based on the reactants and products. Synthesis A + B --> AB Decomposition AB -->A+B Single replacement A + BC --> AC + B Double replacement AB + CD --> AD + CB Exothermic reaction a chemical reaction in which heat or energy is released to the surroundings Endothermic reaction A reaction that ABSORBS energy in the form of heat 4Fe + 3O2 --> 2Fe2O3 It is exothermic because energy is released. It has less energy than the iron and oxygen by itself. Acids donate protons (in the form of hydrogen ions) and generally taste sour, turn litmus paper red, and act corrosively. bases accept protons (or hydrogen ions) in solution and generally taste bitter, turn litmus paper blue, are very corrosive, and will be slippery in solution. neutralization reaction occurs when an acid and a base react to form a salt and water. Strong acids completely ionize in solution strong bases dissociate in solution