2.S: Atoms, Molecules, and Ions (Summary)
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2.1: The Atomic Theory of Matter
- Dalton’s atomic theory of matter:
- Each element is composed of extremely small particles called atoms
- All atoms of a given element are identical; the atoms of different elements are different and have different properties
- Atoms of an element are not changed into different types of atoms by chemical reactions
- Compounds are formed when atoms of more than one element combine
- explains the law of constant composition, law of conservation of mass
2.2: The Discovery of Atomic Structure
- subatomic particles – what atoms are composed of
- Like charges repel each other; unlike charges attract
Cathode Rays and Electrons
- cathode rays – radiation resulting from a high voltage
- cause certain materials to give off light (fluoresce)
- mass of an electron 9.10939*10-28g
- 2000 times smaller than hydrogen
1.2.2 Radioactivity
- radioactivity – spontaneous emission of radiation
- three types of radiation: alpha (a ), beta (b ), gamma (g )
- alpha and beta radiation are affected by an electric field
- beta particles have a charge of 1-
- alpha particles have a charge of 2+
- gamma radiation has no particles and no charge
1.2.3 The Nuclear Atom
- Rutherford determined that there was a nucleus in every atom
- Protons discovered by Rutherford in 1919
- Neutrons discovered by James Chadwich in 1932
2.3: The Modern View of Atomic Structure
- charge of an electron is –1.602*10-19
- charge of a proton is +1.602*10-19
- 1.602*10-19 is called to electronic charge
Particle | Charge | Mass (amu) |
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Proton | Positive | 1.0073 |
Neutron | None | 1.0087 |
Electron | Negative | 5.486*10-4 |
- atomic mass unit (amu) – equals 1.66054*10-24 grams
- angstrom (Å) – unit of length to measure atomic dimensions
- 1 angstrom = 10-10m
- atoms have diameters of 1-5 Å
- nucleus – diameter of 10-4 Å
2.4: Atomic Mass
- all atoms of an element have the same number of protons in the nucleus
- isotopes - atoms of the same element that have a different number of neutrons
- atomic number – the number of protons in an atom
- mass number – number of protons + number of neutrons
- nuclide – atom of a specific isotope
2.5: The Periodic Table
- periodic table – the arrangement of all the elements by atomic number and similarities into a table
- columns = groups
- metallic elements – all elements on the left side and in the middle of the periodic table
- nonmetallic elements – elements on the periodic table that are divided by a diagonal steplike line from boron to astatine
- metalloids – properties of metals and nonmetals
2.6: Molecules and Molecular Compounds
- molecule – two or more atoms bonded together
- Molecules and Chemical Formulas
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- chemical formula – way of representing molecules
- diatomic molecule – any molecule made up of two atoms
- molecular compounds – contains more than one type of atom
- Molecular and Empirical Formulas
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- molecular formulas – chemical formulas that indication the actual number of atoms
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- empirical formula – chemical formulas that only give the relative number of atoms
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- Picturing Molecules
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- structural formulas – shows which atoms are attached to other atoms
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- perspective drawing – gives an idea of the three-dimensional shape of a molecule
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- ball-and-stick models – shows atoms as balls bonded by sticks
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- space-filling model – accurate representation of what atoms would look like
2.7: Ions and Ionic Compounds
- ion – charged particle formed by the removal or addition of an electron
- cation – ion with a positive charge
- anion – ion with a negative charge
- metal atoms tend to lose electrons
- nonmetal atoms tend to gain electrons
- polyatomic ions – joined atoms that have a net positive or negative charge
- Predicting Ionic Charges
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- alkalie metals form 1+ ions
- alkaline earth from 2+ ions
- halogens form 1- ions
- group 6A from 2- ions
- Ionic Compounds
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- ionic compound – a compound that contains positively and negatively charged ions
- ionic compounds are generally combinations of metals and nonmetals
- molecular compounds are generally nonmetals only
2.8: Naming Inorganic Compounds
- chemical nomenclature – the naming of substances
- over 10 million known chemical substances
- organic compounds – contain carbon
- inorganic compounds – everything else
- positive ions
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- cations formed from atoms have the same name as the metal
- if a metal can form cations of differing charges, the positive charge is given by a roman numeral in parentheses following the name of the metal
- cations formed from nonmetal atoms have names that end in –ium
- Negative Ions
- monatomic anions have names formed by dropping the ending of the name of the element and adding the ending –ide
- polyatomic anions containing oxygen have names ending in –ate or –ite
- called oxyanions
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- anions derived by adding H+ to an oxyanion are named by adding as a prefix the word hydrogen or dihydrogen, as appropriate
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- Ionic compounds
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- names of ionic compounds are the cation name followed by the anion name
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- Names and formulas of Acids
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- acids bases on anions whose names end in –ide have associated acids that have the hydro- prefix and an –ic ending
- acids based on anions whose names end in –ate or -ite
Anion | Acid |
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____ide | Hydro____ic acid |
____ate | _____ic acid |
____ite | _____ous acid |
- Names and Formulas of Binary Molecular Compounds
- the name of the element farthest to the left in the periodic table is usually written first
- if elements in same group lower one written first
- name of second element is given an –ide ending
- greek prefixes used to indicate number of atoms of each element
- if prefix ends in a or o and the name of the anion begins with a vowel, the a or o is dropped
Prefix | Meaning |
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Mono- | 1 |
Di- | 2 |
Tri- | 3 |
Tetra- | 4 |
Penta- | 5 |
Hexa- | 6 |
Hepta- | 7 |
Octa- | 8 |
Nona- | 9 |
Deca- | 10 |