Ch2.Water and carbon : the chemical basis of life
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How did life begin on earth?
The theory of chemical evolution suggests that simple chemicals in ancient earth combined to form larger, more complex molecules. They used energy from sunlight and geothermal sources to make chemical bonds.
- -basic building blocks for all molecules
- -all have nucleus (carries weight)
- -you can find protons and neutrons
- - #protons = #electrons
- -protons+neutrons= mass #
- -electrons orbit around nucleus
- -protons (positive charge), electrons negative
- -valence shells (electrons can be shared or donated)
atoms join by forming bonds to make molecules.
What is a covalent bond?
When two atoms share their electrons they form a covalent bond.
- -A covalent bond has two electrons in it, one from each atom. When both atoms share electrons equally, the covalent bond is nonpolar. When one atom attracts electrons more towards it, the covalent bond becomes polar (the bond is polarized. The two ends are not similar).
- -Covalent bonds can be single, double or triple bonds.
When atoms lose or gain electrons, they become ions.
When atom gains electrons
it becomes a negatively charged ion (anion=an-‐ion).
When atom LOSES electrons
becomes positively charged ion (cation=cat-‐ion).
- Positive charge is attracted to negative charge ion.
- -this is a ionic bond between cation and an anion.
Water is a good solvent because...?
- 1. It can help dissolve substances (solutes).
- 2. allows polar molecules and ions to mix with water.
How do chemical reactions happen?
Reactants react with each other to generate products. A chemical reaction comes to a dynamic equilibrium when it happens in both directions at the same rate.
Reactions that absorb heat
Reactions that release heat
Two forms of energy?
- -Potential (hidden energy)
- -Kinetic (motion or active energy)
- -Reactant has less energy than product (absorbs energy)
- -Endothermic reactions absorb heat
- -Reactants have more energy than product (exert energy)
- -Exothermic=releases heat.
Difference between Endergonic and Exergonic
- Endergonic: The entropy change (ΔS) is positive.
- Exergonic: Potential energy change (ΔH) is negative.
Gibbs Free Energy Change (ΔG)
*If ΔG is a negative value, reaction happens spontaneously.
-molecules that contain carbon
- -4 electrons in valence shell
- -can form many bonds (single, double or triple, polar or nonpolar)
- -carbon-carbon bonds important step to chemical evolution
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