Compounds and molecules: by PvU21amT

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									      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    • Water is a liquid at room
  bend, stretch, and      temperature because of
  rotate without          the attraction between
  breaking.               water molecules.
• The strength of all
  chemical bonds is
  different, that
  depends on type of
  molecule.
  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 dioxide-
  quartz. 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:
                    Ionic             Covalent
                    compounds         compounds
  •
Structure           Net work of       molecules
                    bonded ions
Valence electrons   Get transferred   shared
Electrical          Good only         poor
conductivity        when melted
                    or dissolved
State at room       Solids only    Solid, liquid,
temperature                        or gas
Melting & boiling   Generally high Generally low
points
                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):
•   Ion name and symbol   Ion Charge
•   Cesium ion, Cs+            1+
•   Lithium ion, Li+
•   Potassium ion, K+
•   Rubidium ion, Rb+
•   Sodium ion, Na+
•   Barium ion, Ba2+          2+
•   Beryllium ion, Be2+
•   Calcium ion, Ca2+
•   Magnesium ion, Mg2+
•   Strontium ion, Sr2+
•   Aluminum ion, Al3+        3+
Some common anions (negative ions):
•   Element            Ion             Ion charge
•    Fluorine,F     fluoride ion, F−      1−
•    Chlorine, Cl    chloride ion, Cl−
•   Bromine, Br      bromide ion, Br−
•   Iodine, I        iodide ion, I−
•   Oxygen, O        oxide ion, O2−       2−
•   Sulfur, S        sulfide ion, S2−
•   Nitrogen, N      nitride ion, N3−     3−
Some common transition metal cations
•   name                  Ion symbol
•   Copper(I) ion          Cu+
•   Copper(II) ion         Cu2+
•   Iron(II) ion           Fe2+
•   Iron(III) ion          Fe3+
•   Nickel(II) ion         Ni2+
•   Nickel(III) ion        Ni3+
•   Chromium(II) ion       Cr2+
•   Chromium(III) ion      Cr3+
•   Cadmium(II) ion        Cd2+
•   Titanium(II) ion        Ti2+
•   Titanium(III) ion       Ti3+
•   Titanium(IV) ion        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   1) For covalent
  covalent compounds:      compounds of two
                           nonmetals-elements,
Prefix     # of atoms      numerical prefixes tell
• Mono-    1               how many atoms of
• Di-      2               each element are in the
• Tri      3               molecule.
• Tetra-   4             2) Name positive ion first
• Penta-   5               followed by negative ion
• Hexa     6             3) Numerical prefixes are
• Hepta    7               used before name of
• Octa-    8               ions and “ide” suffix is
• Nona-    9               used at ending anions.
• Deca-    10            Ex: N2O4 =
                         Dinitrogen tetra oxide.
Compounds      Empirical formula Molar mass    Molecule-formula
Formaldehyde     CH2O           30.03 g/mol     CH2O
Acetic acid      CH2O           60.06 g/mol     2 × CH2O
                                                = C2H4O2
Glucose          CH2O           180.18 g/mol    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:
•   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.
•   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.

								
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