Chemistry Review Chapters 1 2

Therefore the rings of electrons underneath the valence atoms shield the valence electrons from the nucleus so that the atom isn’t pulled in as tight as the one before it. o Trends for atomic size: As you go down a periodic table, atoms get smaller Because the protons increase as you go down a period, the positive charge on tighter to the nucleus rather looser. o Trends for ionization energy: Ionization energy tends to go down a group o As you go down a period the attraction between the nucleus and the electrons in the outer energy level decreases. o Ionization energy tends to increase across a period. o As you go across a period the attraction between the nucleus and the electrons in the outer energy level increases. Therefore, more energy is needed to pull an electron away from its atom. Lewis structure: a symbolic representation of the arrangement of the valence electrons of an element  · Octet: an arrangement of eight electrons in the valence shell of an atom  · Ioniza tion energy: the energy that is needed to remove an electron from a neutral atom  · Atomic mass unit (u): a unit of mass that is 1/12 of the mass of a carbon-12  · Radioisotope: an unstable isotope of an element, which undergoes radioactive decay  · Mass number: The total number of protons and neutrons in the nucleus of one of its atoms. Each proton or neutron is counted as one unit of the mass number. Energy level: fixed, three-dimensional volume in which electrons travel around the nucleus.  · Valence electron: an electron that occupies the outermost energy level of an atom.  · Stable octet: an arrangement of eight electrons in the valence shell of an atom.  · Electron affinity: the change in energy that accompanies the addition of an electron to an atom in the gaseous state.  · Cation: a positively charged atom.  · Anion: a negatively charged atom. Theories: Law of Conservation of mass: During a chemical reaction, the total mass of the substances involved does not change. Law of Definite Proportions: Elements always combine to form compounds in fixed proportions by mass. (Eg. Water always contains the elements hydrogen and oxygen combined in the following proportions: 11% hydrogen, 89% oxygen) Lesson 3 Ionic and Covalent compounds  · Chemical Bonds: the forces that attract to each other in compounds. o BONDING INVOLVES THE INTERACTION BETWEEN THE VALENCE ELECTRONS OF ATOMS WHICH USUALLY CREATES A MORE STABLE BOND THAT AN ELEMENT ON ITS OWN.  · Ionic compound: between a non-metal and a metal where the metal loses an electron and the non-metal gains it Characteristics of an ionic bond consist of:  § Normally happens between a metal and a non-metal  · Metals tend to lose electrons, non-metals tend to gain them.  § Very high melting point  § Easily dissolved in water  § Good conductor of electricity, in water or on its own.  · Covalent compound: a bond between two non-metals (or a metal and a non-metal when the metal has a high electron af finity), where atoms share electrons o Characteristics of a covalent bond consist of:  § Low melting point  § When contained under high pressures or temperatures, becomes liquid  § Weak conductor of electricity Somewhat soluble o Polar covalent compound: a bond where the electronegativity is not great enough to completely bond to the other atom. Although, it does move closer to an atom, it never completely bonds. (between 0. 5 and 1. 7) This therefore means that when the electrons are partially exchanged, rather than having a + or – sign, they receive a ? + or ? – symbol  · Electronegativity: the measure of an atoms ability to attract electrons in a chemical bond. (EN) the opposite of atomic size which therefore means that as the atomic size increase, the electronegativity decreases If the electronegativity difference is 0. 00-1. 6 the bond is covalent. o If the electronegativity difference is over 1. 7 and up the bond is ionic.  · Octet rule: atoms bond in o rder to achieve an electron configuration that is the same as the electron configuration a noble gas. (8 valence electrons)  · Isoelectric: when two atoms or ions have the same electron configuration. (e. g. Cl and Ar)  · Molecular compounds: See covalent bonds  · Intramolecular forces: the forces that bond covalent bonds together  · Intermolecular forces: the forces that bond ionic bonds together Metallic bonding: in order to combine two metals both metals lose their valence electrons and combine them in a free flowing â€Å"sea† of electrons so that the electrons are shared equally by all atoms that join the bond.  · Alloy: a homogeneous mixture of two or more metals.  · Lone pairs: electron pairs that are not involved in bonding  · Bonding pairs: electron pair that are involved with bonding.  · Polar molecule: a molecule with a partial negative charge on one end and a partial positive charge on the other end.  · Non-polar molecule: a molecule that has nei ther a positive nor negative end.