Chapter no. 2 Water and Carbon-The Chemical Basics of Life
Ions,Atoms and Molecules
• all matter is 96% Hydrogen, carbon, oxygen and nitrogen.
• Dalton-a unit ot represent mass of proton, neutron and electron in grams.
Aarrangement of electrons
• Electrons move around around in atomic nuclei in specific regions called orbits.
• each orbital can hold upto two electrons.
• Orbitals are grouped into levels called electron shells.
• Electron shells are numbered with the smallest number being closest to nucleus.
• Each electron shell contains a specific number of orbits.
• The electrons of an atom fill the innermost shell first,before filling outer shells.
• Valence Shells-outermost shell of an atom.
• Valence Electrons- electrons in the outermost shell of an atom.
• Chemical Bonds-strong sttractions that bind atoms together.
• An atom is most stable when it valence shell is filled. Shell can be filled through
the formation of chemical bond.
• Molecules-substances held together by covalent bond.
• Two types of covalent bonds:
1. Polar covalent bond-an unequal sharing of electrons between atoms,bond is
asymmetric e.g. in H2O due to high electronegativity of oxygen, it holds the
electrons more closesly and gains a partial negative charge whereas hydrogens
gain a partial positive charge.However, the net charge is zero.
2. Non-Polar covalent bond-electrons are shared equally between atoms, bond is
• electronegativity-the ability of an atom to attract electrons.
• oxygen is highly electronegative atom. • ionic bonds-the bond formed between two atoms by completely transfering an electron
from one atom to the other.
• Ion-an atom or molecule that carries charge.
• Two types of ions:
3. Cations-positively charged ions.
4. Anions-negatively charged ions.
• Ionic Bonding
When an ionic bond is formed, electrons are completely transferred from one atom to
another.As a result, the atom donating its electron gains a positive charge and becomes a
cation. On the other hand, the atom gaining this electron gains a negative charge and
becomes an anion.
• the elctrical attraction between the ions is very strong.
• Electron sharing continum-degree to which electrons are shared in chemical bonds.
• equal sharing (non-polar covalent) same electronegativity.
• unequal sharing (polar covalent) one atom more electronegative.
• total transfer (ionic bond) very strong electronegativities.
• Methane-CH4: Tetrahedral in shapes, structure with four triangular surfaces.
• Water-H20: bent and two dimensional or planar.
• Molecular Formulas-no. and type of atoms in a molecule.
• Structural Formulas-indicate which atoms are bonded together and whether the bonds
are single, double or tripls-good for planar molecules.
• Ball and Stick Models-provide information on 3D structures of molecules, also indicate
the relatives sizes of atoms involved.
• Space Filling Models-difficult to read but accurately depict the spatial relationships
• When a chemical reaction occurs, one substance is combined with other or broken down into another substance.Atoms are rearranged in molecules; in most cases, chemical bonds
are broken and new bonds bonds form.
The Early Oceans and Properties of Water
• 75% of a cellès volumes is water.
• 70% of human body is water.
Properties of Water
5. Great Solvent- e.g. NaCL dissolving in H2O.
6. Cohesion,Adhesion and Surface Tension- i.e. binding between water molecules.
7. Density- becomes lighter upon becoming solid.
8. High capacity for absorbing energy,
9. Ability to dissociate
• Hydrogen bond-weak electrical bond between partial positive charge on one H2O
colecule and partial negative charge on another H2O.
• forms,breaks apart with addition or subtraction of heat.
• Hydrophilic (water-loving): substances that for H-bonds with water.
• Hydrophobic (water-fearing): substances that do not interact with water.
• Hydrogen bonding makes it possible for almost any charged or polar mol