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Anion
- a negatively charged ion, such as Cl-
- gained 1 or more electrons
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Cation
- a positively charged ion, such as Na+
- lost 1 or more electrons
- all are from metals including H+ and NH4+
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Covalent compound
- a combination of atoms in which noble gas arrangements are attained by sharing electrons
- shared valence electrons
- 2 non-metals:
- writing electron dots:
- - exist list - total # valence electrons from all atoms in the compound, plus/minus charge
- - wish list - total # electrons that all atoms in compound would like to have (nearest noble gas)
- - wish list - exist list = # of bonding electrons
- naming:
- - end in -ide
- - use Greek prefixes to show how many of each atom needed. Mono- may be left off 1st atom.
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Dipole
the separation of positive and negative charges in a polar bond indicated by an arrow that is drawn from the more positive atom to the more
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negative atom
- covalent molecules where one end of it is + and the other end of the molecule is - because:
- - there is at least one polar covalent bond in the molecule
- - the molecule is asymmetrical or uneven in its shape
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Dipole-dipole attraction
attractive forces between oppositely charged ends of polar molecules
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Dispersion forces
- weak dipole bonding that results from momentary polarization of non-polar molecules
- aka London forces, Van De Walls forces
- weak forces from temporary dipoles between non-dipoles (happens occassionally when an electron orbits one bonded atom more than the other bonded one)
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Double bond
a sharing of 2 pairs of electrons by 2 atoms
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Electronegativity
the relative ability of a element to attract electrons in a bond
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Electronegativity difference rule
- <0.4 => non-polar covalent bond
- 0.4 - 1.8 => polar covalent bond
- > 1.8 => ionic bond
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Formula
the group of symbols and subscripts that represents the atoms of ions in a compound
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Hydrogen bond
the attraction between a partially positive H atom and a strongly electronegative atom of F, O or N.
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Intermolecular forces (attractive forces in compounds)
- in order of decreasing strength:
- - hydrogen bonding
- - dipole-dipole attraction (for polar molecules)
- - dispersion forces
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Ion
- an atom or group of atoms hanving an electrical charge because of a loss or gain of electrons
- charged atom or group of atoms because of a loss or gain of electrons
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Ionic bond
- a simple attraction between 2 opposite charged ions after their atoms have transferred or exchanged electrons
- metal with non-metal
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Ionic charge
the difference between the number of protons (positive) and the number of electrons (negative) written in the upper right corner of the symbol for
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the element or polyatomic ion
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Ionic compound
- a compund of positive and negative ions held together by ionic bonds
- writing binary ionic compounds:
- - the + metal ion is always placed 1st, the non-metal - ion is placed last; the compund ends in -ide
- compounds whose metals have variable charges:
- - roman numeral after metal indicates charge (+) of metal.
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Molecule
the smallest unit of 2 or more atoms held together by covalent bonds
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Non-polar covalent bond
a covalent bond in which the electrons are shared equally between the atoms
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Non-polar molecule
a molecule that has only non-polar bonds or in which the bond dipoles cancel
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Octet
a set of 8 valence electrons
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Octet rule
- elements in Groups 1A-7A (1, 2, 13-17) react with other elements by forming ionic or covalent bonds to produce a noble gas arrangement
- usually 8 electrons in the outer shell
- atoms react such that they gain, lose or share electrons so as to have a total of 8 electrons in their valence (noble gas configuration)
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Polar covalent bond
a covalent bond in which the electrons are shared unequally between atoms
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Polar molecule
a molecule containing bond dipoles that do not cancel
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Polarity
a measure of the unequal sharing of electrons indicated by the difference in electronegativity
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Polyatomic ion
- a group of covalently bonded non-metal atoms that has an overall electrical charge
- ions composed of many (> 2) atoms, but act as a single ion with a single overall charge
- many are oxyanions
- many end in -ate or -ite; exceptions - Hydroxide OH-, cyanide CN-, ammonium NH4+ (cation)
- Naming:
- - metal placed 1st
- - polyatomic ion is placed last and is recognized as such, eg parenthesize if > 1 ion (needs subscript)
- hint - if ther are 3 types of atoms in the molecultes, then 90% of the time there is a polyatomic ion
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Triple bond
a sharing of 3 pairs of electrons by 2 atoms
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Valence-shell electron-pair repulsion (VESPR) theory
a theory that predicts the shape of a molecule by placing the electron pairs on a central atom as far apart as possible to minimize the mutual repulsion of the electrons
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