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Chapter 4: Chemical Basis of Life.

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Presentation on theme: "Chapter 4: Chemical Basis of Life."— Presentation transcript:

1 Chapter 4: Chemical Basis of Life

2 Atom: the basic unit of matter

3 Composition of Matter: Subatomic Particles
Proton, Neutron & Electron Proton = (+) {defines the atom) Electron = (-) Neutron = no charge Protons and Nuetrons are located in the nucleus Electrons are not found in the nucleus – They travel at high speeds throughout the atom in a series of distinct energy levels that surround the nucleus. The existence of these electrons is extremely important in determining the chemical properties of an atom.

4 An Element: Element – a pure substance that consists entirely of one type of atom. They are represented by a one or two letter symbol on the periodic table. Atomic # = # protons Atomic mass = mass of nucleus (p + n)

5 What Is An Isotope? The number of protons will never change, but the number of neutrons can vary from atom to the next. Isotopes of an atom differ in neutron number. (# Protons ≠ # neutrons)

6 Radioisotopes Some larger isotopes are unstable and decay giving off radiation (matter & energy) Such isotopes are useful in research and medicine “Biological spies” for body scans Radiation treatment for cancer

7 Chemical Compounds Produced when elements combine to form substances consisting of two or more atoms. Represented by chemical formulas: Water (H2O), Table Salt (NaCl), Sulfuric Acid (H2SO4) Multiple Molecules: Single Molecule :

8 Forming Bonds: Share or Transfer Electrons
In order to achieve stability – an atom will either transfer or share electrons (valence) This is achieved through either ionic or covalent bonding.

9 Ionic Bonding Ionic bonding – involves the transfer of electrons from one atom to another (gain or lose). Ex: NaCl

10 Covalent Bonding chemical bond formed by the sharing of electrons.
No elements are gaining or losing atoms. Ex. H20

11 Chemical Reactions Atoms within molecules are rearranged to produce new molecules: Bonds are broken Atoms are rearranged New bonds are formed As the law of conservation of mass tells us, matter is not created nor destroyed during a chemical reaction. Some reactions absorb more energy than they release (endergonic/endothermic) Other reactions release more energy than they absorb (exergonic/exothermic)

12 Water: One of the few naturally occurring
compounds that is liquid at the temperatures found on the Earth’s surface. Expands as it changes from liquid to solid. This is why ice floats on lakes and rivers High Heat Capacity – resists change in temperature (a lot of energy stored/released for temp change) High Heat of Vaporization – evaporation requires a lot of energy

13 Water – A Polar Molecule
Water has an uneven distribution of electrons Since Oxygen is a bigger atom (more protons) than the hydrogen atoms, the electrons spend more time near the oxygen This creates a partial charge on each end This partial charge holds individual water molecules together, makes water excellent at dissolving.

14 Hydrogen Bonds Because of their partial positive & negative charges, polar molecules like water can attract each other. The hydrogen atom of one water being attracted to the oxygen atom of another water is an example of hydrogen bonding.

15 Water acts like a magnet….

16 Cohesion, Adhesion & Capillary Action
Cohesion: attraction (by H-bonding) between two molecules of the same polar substance Adhesion: attraction (by H-bonding) between two molecules of the different polar substances Capillary Action: ability of water to rise in a narrow tube against the force of gravity

17 Surface Tension

18 Mixtures The charged regions of water molecules make them good at forming mixtures A mixture is a substance composed of two or more elements or compounds that are mixed but not chemically combined Ex: salt and pepper stirred together Mixtures made with water are called solutions and suspensions.

19 Solutions Solution: a homogenous mixture in which one substance is dissolved into another A solute (like sugar) completely dissolves in a solvent (like water) like in iced tea. Water is the best (universal) solvent due to it’s polarity (charged ends)


21 Suspensions Materials do not break up into individual atoms, but particles are small enough that they do not settle on the bottom of a container. Example: blood

22 Solutions: Acids HCl  H+ + Cl- When some compounds dissolve
in water, they break apart into individual ions. HCl  H+ + Cl- Compounds that release hydrogen ions (H+) into a solution are acids; High [H+] [ ] means concentration of Characteristics of Acids (do not write) Produce H+ (H3O+) ions in water Taste sour Corrode metals React with bases to form salts and water Are electrolytes

23 Solution: Bases Bases are compounds that release
hydroxide ions (OH-) into a solution NaOH  Na+ + OH- Produce OH- ions in water Characteristics of Bases (do not write) Taste bitter, chalky Are electrolytes (produce electricity) Feel soapy, slippery React with acids to form salts and water

24 7 is a neutral pH [H+] = [OH-] pH < 7 = acid pH > 7 = base Farther pH from 7, the more acidic or basic Every change in pH value corresponds to a ten-fold change in [H+] Ex) pH 3 is 10x more acidic than pH 4

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