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UMass Amherst CHEM 110 - Chemistry Chapter 2

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Chemistry Chapter 2Part 1● Atoms have a nucleus with protons and neutrons surrounded by electrons that movearound the nucleus so fast that they create an electron cloud.● Atoms are about 10-10m (1 Angstrom) in diameter.● Protons: Subatomic particle with a positive charge(+1) and has a mass = 1.6726 x10-24 g or 1 atomic mass unit(amu)● Neutrons: Subatomic particles with no charge and have a mass of 1 amu. Stabilizes thenucleus and moves the protons far away from each other.● Electron: Subatomic particle with a negative charge(-1) and has a mass = 9.1096 x10-31 or .000549 amu(very small so = 0).● Atomic Number: It is equal to the number of protons. All atoms of the same elementhave the same number of protons. In neutral atoms number of protons = number ofelectrons. It is a one or two lettered symbol to represent an element with the massnumber and atomic number.● Mass number: It is equal to number of protons + number of neutrons. Mass number canchange for different atoms of the element.○ Ex: Written as Nitrogen-15 atom(7 protons, 8 neutrons)● Atomic nucleus: A very small region of the atom that is dense and holds protons andneutrons.● Electrons account for most of the volume of atoms.● Atom has a neutral charge because it has the same number of protons and electronsand charges cancel each other out.● Isotopes: Atoms with same atomic number (same number of protons), but differentmass number (different number of neutrons).○ Ex: Nitrogen-15 atom(7 protons, 8 neutrons)● Percent abundance: The percentage of atoms of a natural sample of the pure elementrepresented by a particular isotope, to describe isotope composition.● Atomic weight: Average mass of all naturally occurring isotopes taking in account therelative abundance.○ Atomic weight = (% Abundance of isotope A/100 ) × mass of isotope A + (%Abundance of isotope B/100 ) × mass of isotope B● Dimitri Mendeleev (1834 – 1907) developed the modern periodic table.● There 118 known elements:○ 83 are stable and found in nature○ 7 are found in nature but are radioactive○ 24+ are not naturally found on earth in significant amounts● Groups: Vertical columns.○ Number of valence electrons = group number.● Periods: Horizontal rows.○ Elements in the same group have similar physical and chemical properties.● Alkali metals: Group 1A, shiny solids that react vigorously with air, H20, and halogens.● Alkaline earth metals: Group 2A, most react with H20 to form alkaline solutions.● Chalcogens: Group 6A.● Halogens: Group 7A, nonmetals, highly reactive. Called molecules.● Noble gases: Group 8A, all gases at room temperature, least reactive elements.● From left to right on the periodic table, the elements get less metallic. Called discreteatoms.● Metals have loosely held electrons, weak pull of electrons.● Main group elements: The representative elements, Group A.● Transition metals: Group B elements.● Lanthanides: Portion of period 6 (57 – 71)● Actinides: Portion of period 7 (89 – 103)● Metals: Elements of the left of the periodic table, generally shiny and ductile and goodconductors. Called metallic lattice.● Nonmetals: Elements on the right of the periodic table, dull brittle, mostly gases orsolids, do not conduct electricity. Called molecules, except noble gases.● Metalloids: Elements of the interface of these 2 regions, called semi-metals, haveproperties of metals and nonmetals.● Valence electrons: Electrons found in the outermost shell of the element.● Core electrons: Any other electrons in an atom, located deeper down.● Ionic Bonding: Metals and non metals.● Covalent/molecular bonding: Only non metals. Happens when two or more non metalsbond with each other and share their electrons.● Cations: positively charged ions (formed when an atom loses electrons).● Anions: negatively charged ions (formed when an atom gains electrons).● In neutral compounds total cationic charge equals total anionic charge● Ionic Bond: Type of bond formed between cation and anion.● Monatomic Ions: When atoms gain or lose electrons.● Naming Monoatomic Ions & Cations:○ Cations: Name of the element followed by cation/ion■ Example: K+ is called potassium cation/ion■ Al+3 is called aluminum cation/ion○ Transition metal cations: Name of the element (charge in roman numerals)followed by cation/ion■ Example: Cr+2 is called chromium(II) cation and Cr+3 is calledchromium(III)■ cation Co+2 is called cobalt (II) cation■ Co+3 is called cobalt (III) cation● Naming Monoatomic Ions & Anions:○ Root name of the element followed by -ide■ Ex: Anion of Hydrogen = hydride.■ Ex: Anion of Oxygen = oxide.● Polyatomic Ions: Group of atoms that have a charge(positive or negative)● Ionic Compounds Formula and Naming:○ Ionic compounds are represented by the simplest ratio of cation to anion.○ Rule 1: In an ionic compound cation is written first, followed by anion○ Rule 2: In neutral ionic compounds total cationic positive charge is balanced bytotal anionic negative charge● Naming Covalent Compounds○ Rule 1: First word of the compound name is the first element in the compound○ Rule 2: The second word in the compound name is the second element with -ide○ Rule 3: Use prefix to show how many atoms of each type■NumberPrefix1mono2di3tri4tetra5penta6hexa7hepta8octa9nona10deca12dodeca○● Rule 4: Don’t use “mono” on first element● Allotropes: Different forms of the same element that differ in physical and chemicalproperties.● Inorganic Acids: Inorganic acids produce H+ when dissolved in water.● In general, hydrogen is the first element in the formula of inorganic


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