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The flashcards below were created by user
murphyainec
on FreezingBlue Flashcards.
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define compound
substance that is made up of two or more different elements chemically combined
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define chemical bonds
attractive force that holds atoms together
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state the octet rule
when bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost shell
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exceptions to octet rule
- >transition metals
- >elements near helium (hydrogen, lithium etc)
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define ion
charged atom or group of atoms
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define ionic bond
force of attraction between oppositely charged ions in a compound
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what is crystal lattice
three-dimensional arrangement of ions
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define chemical formula
way of representing a compound using symbols for the atoms present and numbers to show how many atoms of each element are present
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hydrogencarbonate ion
HCO3-
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why do transition metals have variable valency?
there is such a small energy difference between the 4s and thr 3d subshell
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ends in -ide
compound that just contains two elements
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ends in -ate
contains oxygen as well as the other two elements
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why are scandium and zinc not considered transition metals?
- >scandium can only form Sc3+ ions and zinc can only form Zn2+ions
- >they only form white compounds
- >shows little catalytic activity
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define transition metals
forms at least one ion with a partially filled d subshell
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when are ionic compounds normally formed?
when metals react with non-metals
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define molecule
group of atoms joined together
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what is a covalent bond
sharing of a pair of electrons
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define valency of an element
number of atoms of hydrogen or any other monovalent element with which each atom of the element combines
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sigma bond
head on overlapping
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characteristics of ionic compounds
- >difficult to cut
- >usually hard and brittle
- >contain a network of ions in the crystal
- >high melting point
- >high boiling point
- >usually solid at room temp
- >conduct electricity when molten or dissolved in water
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characteristic of covalent compound
- >contain individual molecules
- >usually soft
- >low melting point
- >low boiling point
- >usually liquids, gases or soft solid at r.t
- >do not conduct electricity
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what does VSEPR stand for?
valence shell electron pair repulsion theory
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what does the VSEPR theory state?
shape of a molecule depends on the number of pairs of electrons in the valence shell of the central atom
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define electronegativity
relative attraction that an atom in a molecule has for a shared pair of electrons in a covalent bond
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uses of electronegativity values
- >to predict polarity of covalent bonds
- >to predict which compounds are ionic and which are covalent
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what is a polar molecule
centre of positive charge and the centre of negative charge coincide
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electronegativity difference of more that 1.7
ionic bonding
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electronegativity difference of less than 1.7 or equal to
covalent
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exceptions to the 1.7 rule
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define van der waals forces
weak attractive forces between molecules resulting from the formation of temporary dipoles
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define dipole-dipole forces
force of attraction between the negative pole of one molecule and the positive pole of another
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what does hydrogen bond with
N, O, F
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