Transcript Compounds and molecules: - Wikispaces

Compounds and molecules:
• Molecule is made of two or more atoms that
are chemically bonded.
• compound is made of two or more elements
that are chemically bonded.
• Chemical bonds are the forces that hold
atoms or ions together in a compound.
• Chemical structure is the way, the atoms or
ions are arranged in a substance.
• Bond length is the distance between the
nuclei of two bonded atoms.
• Bond angle is the angle formed by two bonds
to the same atom.
Chemical bonds, bond length, bond angle
• Chemical bonds can
bend, stretch, and
rotate without
breaking.
• The strength of all
chemical bonds is
different, that
depends on type of
molecule.
• Water is a liquid at room
temperature because of
the attraction between
water molecules.
Characteristics of chemical bonds:
• The ball and stick model shows
the bond angle in a molecule of
H2O
• Bond length is given in picometer(pm) is equal to 1 x 10-12
• The space-filling model of water
shows that each hydrogen atom
takes up less space than the
oxygen atom, It determines the
relative size of atoms in a
compound.
• Structural formula shows the
structure of compound in specific
arrangement of bonded atoms.
Structure of compounds and their
properties:
• The chemical structure of compound
determines the properties of that compound.
• Compounds with network structures are
strong solids like diamonds, silicon dioxidequartz. They have high melting point, rigid,
very hard and inflexible.
• Some network solids are made of bonded
ions like sodium chloride (table salt). The
strong attraction between the oppositely
charged ions give high melting points and
boiling points.
Molecular compound: covalent comp.
• Some compounds are made of molecules.
For example, Sugar-C12H22O11 is molecule.
Like, oxygen-O2, Nitrogen-N2 are molecular
compounds.
• Very weak force of attraction is existing
between molecules, they exist as solids,
liquids or gases. Melting points and boiling
points depend on their physical state and type
of chemical bonds involve in the molecules.
• Water is liquid at room temperature because
of the attractions between water molecules
that is known as Hydrogen bond, and strong
covalent bonds exist in H2O, between H & O
Types of Chemical Bonds
• Octet rule: Each atom try to acquire system
of 8–electrons if possible that is considered as
most stable electron configuration.
• Cause of formation of chemical bonds:
Generally, atoms join to form bonds so that
each atom has a stable electron configuration.
• There are different types of chemical bonds.
– Ionic bonds
– Covalent bonds
– Co-ordinate covalent bonds
– Metallic bonds
Ionic bonds
• Ionic bonds: The attractive force arising
between oppositely charged ions when
electrons are transferred from one atom to
another.
Ionic bonds in ionic compounds:
• In above diagram, the sodium atom has only one
electron in outermost shell, it loses one valence
electron while Chlorine atom gains that electron to
complete its octet-system of 8-electrons. As a result,
NaCl comp. is formed.
• Sodium atom becomes positive ion by losing
electron and Chlorine atom becomes negative ion
by gaining electron. Therefore Na+ and Cl- combine
forming ionic bond between them.
• Ionic compounds are in the form of network. They
don’t conduct electric current in solid state, but on
dissolving or melting they are good conductors of
electric current.
Covalent bonds:
• Covalent bond: A bond is formed when atoms
share one or more pairs of electrons.
Two chlorine atoms (below) share
electrons equally to form a nonpolar covalent bond.
Covalent bonds are often shown as a single line
drawn between two atoms. The model at left
shows that the two chlorine atoms share two
electrons (1-pair). Dots represent electrons that are
not involved in bonding.
Covalent bond……
• Two chlorine atoms (above diagram) share
electrons equally to form a nonpolar covalent
bond.
• Covalent bonds are often shown as a single
line drawn between two atoms. The model at
left shows that the two chlorine atoms share
two electrons (1-pair).
 Dots represent electrons that are not involved
in bonding.
 Shared electron pairs remain exactly in the
center of bonded atoms.
Covalent bonds:
• In formation of covalent bonds, atoms may share
two or three pairs of electrons.
Polar and nonpolar covalent bonds:
• Nonpolar Covalent bonds: Covalent bonds
are formed by sharing equal number of
electrons between two similar atoms are
nonpolar. EX: H-H, Cl-Cl, O=O, N≡N
• Polar Covalent: Covalent bond formed
between two dissimilar atoms is polar
covalent bond. The shared electron pair
remains more towards more electro negative
atom, rather than less electro negative atom.
EX:
H-Cl, H-Br, N-H bonds in NH3
molecule.
Comparing Ionic and Covalent compounds:
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Structure
Valence electrons
Electrical
conductivity
State at room
temperature
Melting & boiling
points
Ionic
compounds
Covalent
compounds
Net work of
bonded ions
Get transferred
Good only
when melted
or dissolved
Solids only
molecules
shared
poor
Solid, liquid,
or gas
Generally high Generally low
Metallic bonds:
• Metallic bond: A bond formed by the
attraction between positively charged metal
ions and the electrons around them.
– The strength of metallic bond is very high.
• Metals are flexible and conduct electric
current well because their atoms and
electrons move freely throughout a metal’s
packed structure.
• All metals, like copper, iron, gold, silver nickel
have metallic bonds.
• All metals are solids except Mercury.
• Ion: An atom caring positive or negative
charge. EX: H+ , N-3 are monoatomic ions.
• Polyatomic ions: An ion positive or negative
made of two or more than two atoms.
• Parentheses group the atoms of a polyatomic
ion in chemical molecules of compounds.
• EX:
NH4+
• Some names of polyatomic anions relate to
the oxygen content of the anion. Most of their
names end with –ite or –ate. In molecule,
[NH4]2CO3 → Ammonium carbonate, [NH4]+1
and [CO3]-2 join to form compound-[NH4]2CO3
Some common polyatomic ions:
Some common cations (positive ions):
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Ion name and symbol
Cesium ion, Cs+
Lithium ion, Li+
Potassium ion, K+
Rubidium ion, Rb+
Sodium ion, Na+
Barium ion, Ba2+
Beryllium ion, Be2+
Calcium ion, Ca2+
Magnesium ion, Mg2+
Strontium ion, Sr2+
Aluminum ion, Al3+
Ion Charge
1+
2+
3+
Some common anions (negative ions):
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Element
Fluorine,F
Chlorine, Cl
Bromine, Br
Iodine, I
Oxygen, O
Sulfur, S
Nitrogen, N
Ion
Ion charge
fluoride ion, F−
1−
chloride ion, Cl−
bromide ion, Br−
iodide ion, I−
oxide ion, O2−
2−
sulfide ion, S2−
nitride ion, N3−
3−
Some common transition metal cations
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name
Copper(I) ion
Copper(II) ion
Iron(II) ion
Iron(III) ion
Nickel(II) ion
Nickel(III) ion
Chromium(II) ion
Chromium(III) ion
Cadmium(II) ion
Titanium(II) ion
Titanium(III) ion
Titanium(IV) ion
Ion symbol
Cu+
Cu2+
Fe2+
Fe3+
Ni2+
Ni3+
Cr2+
Cr3+
Cd2+
Ti2+
Ti3+
Ti4+
Naming Ionic Compounds:
• The names of ionic compounds consist of the
names of metal ion and anion bonded with
together. Ex: NaCl → Sodium chloride
• Name metal ion first followed by negative ion.
Use suffix “ide” with negative ion (anions).
ex: Chlorine → Chloride Oxygen → Oxide
• If metal ion is transition metal, then mention
its oxidation number in roman numbers in
small parenthesis.
• Ex: Cr2O3 → Chromium(III)oxide
• An ionic compounds must have a total charge
zero. Ex: Cr2O3 = 2(Cr) + 3(O)=2(3+)+3(2-)=0
Naming Covalent Compounds:
Prefixes used to name
covalent compounds:
Prefix
• Mono• Di• Tri
• Tetra• Penta• Hexa
• Hepta
• Octa• Nona• Deca-
# of atoms
1
2
3
4
5
6
7
8
9
10
1) For covalent
compounds of two
nonmetals-elements,
numerical prefixes tell
how many atoms of
each element are in the
molecule.
2) Name positive ion first
followed by negative ion
3) Numerical prefixes are
used before name of
ions and “ide” suffix is
used at ending anions.
Ex: N2O4 =
Dinitrogen tetra oxide.
Compounds
Empirical formula Molar mass
Formaldehyde
Acetic acid
CH2O
CH2O
30.03 g/mol
60.06 g/mol
Glucose
CH2O
180.18 g/mol
Molecule-formula
CH2O
2 × CH2O
= C2H4O2
6 × CH2O
= C6H12O6
Empirical formula: The composition of a compound
in terms of the relative numbers and kinds of atoms
in the simple ratio.
Molecular formula: A chemical formula that shows the
number and kinds of atoms in a molecule, but not
the arrangement of atoms.
Molar mass: The mass of one molecule in grams or
sum of atomic masses of total atoms in 1-molecule
in grams. Ex: H2O= 2(H)+1(O)=2(1)+1(16)=18 g/mol
Calculation to find Empirical formula:
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One mole of unknown compound has 36.04
g. of carbon and 6.04 g of hydrogen. What is
the compound’ empirical formula?
1) Write the atomic masses
Atomic masses: carbon=12 g/mol, H= 1g/mol
2) Find the molar ratio by dividing mass of
element by its atomic mass. The molar ratio
of elements in the compound is empirical
formula of compound.
Mole of carbon=36.04 g /12 g/mol = 3 mol
H=6.04g/1g/mol = 6 mol
Answer: E.F = C3H6
Organic compounds:
• Organic compounds: An organic compound is
a covalently bonded compound that contains
carbon excluding carbonates and oxides.
Most organic compounds also contain
hydrogen, oxygen, sulfur, and phosphorus.
• Our body is made of organic compounds,
which play important roles in keeping the
body alive.
• We are using innumerable organic
compounds in everyday life. Ex: alkane,
alkenes, alkynes, aromatic hydrocarbons etc.
Classification of Hydrocarbons:
H.C.→Simplest type of organic compounds
containing only carbon and hydrogen atoms
are called hydrocarbons, abbreviated as H.C.
Hydrocarbons-H.C.
Open chain H.C.
Cyclic H.C.
Alkanes H.C.
Aromatic H.C.
Alkenes H.C.
Alicyclic H.C.
Alkynes H.C.
Chemistry of carbon:
• Carbon has 4-valences, therefore carbon
atoms form four covalent bonds in organic
compounds.
• Arrangement of carbon atoms vary in different
alkanes, alkenes, and alkynes. The structure
of hydrocarbons may be a long chained,
branch chained, or cyclic.
Alkanes:
• Alkanes: All bonds, (c-c and c-H bonds) in the
structure of organic compounds are single covalent
bonds. General formula is CnH2n+2 where n= # of H.
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Alkane Molecular-formula Condensed structural form
Methane CH4
CH4
Ethane
C2H6
CH3CH3
Propane C3H8
CH3CH2CH3
Butane
C4H10
CH3(CH2)2CH3
Pentane C5H12
CH3(CH2)3CH3
Hexane
C6H14
CH3(CH2)4CH3
Heptane C7H16
CH3(CH2)5CH3
Octane
C8H18
CH3(CH2)6CH3
Nonane
C9H20
CH3(CH2)7CH3
Decane
C10H22
CH3(CH2)8CH3
Alkenes and alkynes:
• Carbon atom can join with other carbon atoms
forming single, double or triple covalent
bonds. This is called catenation property of
carbon.
• Alkenes: At least one double bond should be
present between carbon atoms in the
structure of H.C. compound.
Ex:
CH2= CH2 → Ethene
• Alkynes: At least one triple bond should be
present between carbon atoms in the
structure of H.C. compound.
Ex:
CH≡CH→ Ethyne
• Functional group: Atom or group of atoms
present in the given organic compound that is
responsible for all properties of a compound is
called functional group. –OH →hydroxyl group
–Cl → chloro group, -COOH → acidic group
• Alcohols: Organic compounds having
hydroxyl functional group are defined as
alcohols. The names of alcohols end in –ol.
Ex: CH3OH →methanol, C2H5 →ethanol etc.
• Polymers: A large or macro molecule that is
formed by more than five monomers or small
units. Ex: Many ethene molecules combine to
give polymer is called Polyethene. Some
polymers are natural and others are artificial.
Natural polymers:
• Monomer: The smaller molecule that combine
with other similar molecules that makes up
polymer is called a monomer.
• Rubber, wood, cotton, wool, starch, protein,
and DNA are all natural polymers.
• Polymers are widely applicable. For example,
Polypropylene is molded to make plastic
containers, some parts of cars and
appliances. Also used to make carpet, ropes,
and artificial turf for athletic fields.
• A polymer’s structure determines its elasticity.
Biochemical compounds
• Biochemicals, which are essential to life,
include carbohydrates, proteins, and DNA.
• Carbohydrates are compounds which include
sugar and starches and fiber; contains
carbon, hydrogen, & oxygen in their structure
• Carbohydrates provide energy to living
things. Many carbohydrates are made of
glucose and fructose. Starch is polymer chain.
• Protein: An organic compound that is made of
one or more chains of amino acids and that is
a principal component of all cells.
• Amino acid: Simple organic compounds that
contain a carboxyl group and an amino group
and that combine to form proteins.
• DNA: It is a polymer that stores
genetic information. It has a
shape of a twisted ladder known
as double helix. DNA is the
information that the cell uses
to make proteins.
In DNA, cytosine, C, always pairs
Guanine, G. Adenine, A,
pairs with Thymine, T.