Unit 4 Flashcards
How to determine valence electrons?
Group (column) #
Chemical bonds (forces)
Forces that hold atoms together by transfer or sharing electrons
Covalent bond
Electrons are shared resulting in molecule. Polar and non polar
Ionic bond
Formed from ions + or - in which electrons are transferred. + ions are cations, - ions are anions.
Exothermic energy
Energy released from system to surroundings when a bond is formed or broken.
Electronegativity
Ability of the nucleus of one element to attract electrons of another element to obtain an octet.
Electronegativity generally ______ from left to right within a period.
Increases. As size of atom decreases, there is more attraction to nucleus.
Electronegativity generally ______ from top to bottom within a group.
Decreases. The size of the atom increases as more energy levels are added.Bottom left to top right increases.
Higher
/
/ Increases
Lower. /Metals want to lose electrons so they have ____
Low electronegativity. Small attraction for valence electrons.
Nonmetals want to gain electrons so they have _____
High electronegativity. High attraction for valence electrons
The larger the difference between electronegativities of two nonmetals, the more ___ the bond will be
Polar
Ionic bonds en>1.8 in groups ___
1,2,6,7
Polar bonds between 1.8>en>.4
Everything else
Nonpolar covalent bonds if en<.4
C-H only compounds, diatomic elements
Endothermic energy
Absorbed from surroundings to system when a bond is formed or broken.
The reason elements form bonds
Usually to go to lowest energy state
Molecule
Smallest unit of covalently bonded elements
Formula unit
Smallest unit of an ionic bond
Subscripts in a formula give the number of ____ of that element in a molecule.
Atoms
Coefficients
Number in front of a compound giving the total number of molecules of that compound
Ionic bonds
- Electrons are transferred from one atom to another
- ions are formed when electrons are gained or lost
- difference in electronegativity values is great
Cation
Electrons lost-metals
+ion
Anion
Electrons gained-nonmetals
-ion
Formation of ionic bonds is _______
Exothermic
Polyatomic atoms
Charged group of covalently bonded atoms. E entire group will bond to another ion according to its charge, + or -
Nonpolar covalent bonds
Electrons between elements as shared equally. Equal attraction for shared electrons. Balanced distribution of charge. No dipoles
7 diatomics
HOFBrINCl
Noble gases have _____ electronegativity
Zero
Polar covalent bonds
Shared unequally creating dipoles
Polar bond
A covalent bond in which there is an unequal attraction for the shared electrons and the resulting unbalanced distribution of charge
The larger the difference between the electronegativities of two nonmetals the more _____the bond will be
Polar
Oxidation numbers
The real or apparent charge an Atom or ion has when all bonds are assumed to be ionic. (How many electrons would an Atom want to lose or gain to have eight electrons?)
Charged atom
Indicates whether the atom gained electrons (-) or lost electrons (+). Write number followed by + or -. Value indicates how many electrons were gained or lost.
Oxidation number rules
- any atom in free state is 0
- any simple ion is the charge on that ion
- O usually -2, exception peroxides O is -1
- H usually +1, F always -1
A polyatomic ion is equal to
The sum of the individual oxidation numbers
For a neutral molecule, the sum of all charges is equal to
Zero. True of all compounds
Oxidation numbers per group
Group 1=+1
Group 2=+2
Group 3=+3
Hydrides=-1
Group 7=-1 only if bonded with metal. Can have multiple with nonmetals.
Group 6=-2 only with metal. Can have multiple with nonmetals.
Group 5=-3 only with metal. Can have multiple with nonmetals.
Elements with 2 oxidation numbers
- Iron Fe +2 iron ii Fe +3 iron iii
- copper Cu +1 Cu +2
- tin Sn +2 Sn +4
- mercury Hg2 2+ Hg +2
For binary compounds (2 elements) composed of metal (cation) and nonmetal (anion) rules for writing formula (ionic compounds)
-name metal first using full name
-figure charge and put in ( ) if > 1
-name nonmetal 2nd, drop ending and add ide
-no prefixes
Ex:NaCl sodium chloride
Ex: PbCl4 Lead (iv) chloride
Prefixes for number of atoms
1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa
Binary compound of two nonmetals (no ions) chemical formula rules
-least electronegative written first using full name, no prefixes unless more than one atom
-most electronegative is second and always has prefix
-drop ending add ide
-drop final o or a of premix if element starts with vowel
Ex: As2O5 diarsenic pentoxide
Compounds containing polyatomic ions (more than 2 elements) formula rules
-Metals are named first using the full element name
-polyatomic ions retain its name whether its positive or negative
Ex: NH4Cl ammonium chloride
Exceptions to oxidation numbers rules
-peroxides- oxygen with a -1 charge. Nonmetals with O2 is not a peroxide.
Ex: Li2O2 lithium peroxide
CaO2 calcium peroxide
