Chemistry Review sheet: Unit 1- Lesson 1, 2 *Key notes to keep in mind* u Metals have a high low ionization energy u Non-metals have a high electron affinity · Atom: The basic unity of an element which still retains the elements properties · Atomic number: the unique number of protons in the nucleus of a particular element · Isotope: Atoms of the same element which contain a different number of neutrons · Periodic law: The chemical and physical properties of the elements repeat in a regular, periodic pattern when they are arranged according to their atomic number. Periodic trend: a pattern that is evident when elements are organized by their atomic numbers o Trends for atomic size: As you go down a group the atoms get bigger. o As you go down a group, valence electrons occupy and energy level that is farther and farther from the nucleus. 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 · Ionization 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.
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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 affinity), 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 order 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 “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 neither a positive nor negative end.
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