The Chemistry of Life

All life is composed of chemicals

Chemistry - study of matter

Matter is anything that has mass and occupies space.

Atoms are:◦ The smallest units of matter that can exist

separately.

Elements are:◦ Chemical substances composed of the same

kind of atoms.

◦ Each element is represented by a symbol of one or two letters.

Trace elements are equally important

Atoms are composed of:

◦The Atomic Nucleus Protons: + charge Neutrons: 0 charge

◦Electrons: - charge Orbit the nucleus in

energy levels

Atomic Number= the number of protons

Atomic Mass= the sum of protons and neutrons in the nucleus

Charge on the atom:◦ Same # of protons and electrons = neutral charge◦ # of protons does not equal # electrons= ion or charged

atoms

IsotopesAtoms of the same element that have different numbers of neutrons

Remember, isotopes still have the same number of protons!

Radioactive isotopes-How are they formed and what elements can be radioactive?

1) Long-lived radioactive nuclides. Created during the formation of the solar system (~4.6 billion years ago) and are still present in the earth. These include 40K (t½ = 1.28 billion years), 87Rb (t½ = 48.8 billion years), 238U (t½ = 447 billion years), and 186Os (t½ = 2 x 106 billion years, or 2 million billion years).

2) Cosmogenic. Cosmogenic isotopes are a result of cosmic ray activity in the atmosphere. Cosmogenic isotopes are also produced at the surface of the earth by direct cosmic ray irradiation of atoms in solid geologic materials. Examples of cosmogenic nuclides include 14C, 36Cl, 3H, 32Si, and 10Be. Cosmogenic nuclides, since they are produced in the atmosphere or on the surface of the earth and have relatively short half-lives (10 to 30,000 years), are often used for age dating of waters.

3) Anthropogenic Anthropogenic isotopes result from human activities, such as the processing of nuclear fuels, reactor accidents, and nuclear weapons testing. Examples of hydrologically useful anthropogenic isotopes include many of the cosmogenic isotopes mentioned above: 3H, 14C, 36Cl, and 85Kr.

4) Radiogenic Radiogenic isotopes are typically stable daughter isotopes produced from radioactive decay. In the geosciences, radiogenic isotopes help to determine the nature and timing of geological events and processes. Isotopic systems useful in this research are primarily K-Ar, Rb-Sr, Re-Os, Sm-Nd, U-Th-Pb, and the noble gases (4H, 3H-3He, 40Ar).

http://www.sahra.arizona.edu/programs/isotopes/types/radioactive.html

Electrons occupy specific energy levels around the nucleus.

Energy levels hold specific numbers of electrons.◦ First energy level can have up to 2 electrons◦ Next three levels can have up to 8 electrons

Electrons!

Atoms seek to have a full outer energy level (atomic peace)

◦ Atoms that have full outer energy levels are happy or inert

◦ Other atoms seek to fill their outer energy levels through chemical bonds

Molecules consist of two or more atoms joined by a chemical bond◦ Example: H2

Compounds are chemical substances made of two or more elements combined in a fixed ratio◦ Example: H20

Remember: Atoms form chemical bonds to fill their outermost electron energy levels, achieving stability.

There are two ways to achieve this through bonding

________________________

________________________

Atoms can gain or lose electrons to achieve a full outermost energy level

◦ Remember: Atoms in which # protons does not equal # electrons are called ___________.

An ionic bond= the attraction between oppositely charged ions.

Work with your table mate to describe how sodium chloride forms via an ionic bond

◦ Sodium (Na) = 1 electron in outer energy level

◦ Chlorine (Cl)= 7 electrons in outer energy level

◦ Electron donation occurs The positively charged sodium is attracted to the negatively charged chloride

Atoms can achieve full outermost energy levels by sharing electrons instead of exchanging them.

A covalent bond:

◦ is formed by the sharing of electrons.

◦ Single covalent bond-one pair of electrons is shared. Example: H2

◦ Double covalent bond-two pairs of electrons are shared. Example: O2 oxygen

Non-polar covalent bonds: electrons orbit all atoms equally

Polar covalent bonds: electron orbit one or more atoms preferentially due to differences in electronegativity

Oxygen (O) has more protons than hydrogen (H)

Electrons are attracted to O more than H The oxygen end of water is more negative The hydrogen end of water is more positive

Hydrogen bond:

◦ The positive hydrogen end of one polar molecule is attracted to the negative end of another polar molecule.

◦ These are weak bonds that hold molecules together

Hydrogen bonds are very important in biology.

◦ They stabilize the structure of DNA and proteins

◦ And…

-73% of its surface is covered by water (marine &freshwater ecosystems combined).

- Life began in the ocean and the majority of organisms still live there.

Water is the reason that earth is inhabitable

Cell cytoplasm is composed of 73.5% water

1. High surface tension, cohesion and adhesion

Water molecules stick to each other via hydrogen bonds.

Capillary action moves water through streams, soil, animals and plants.

2. Hydrogen bonds in water help resist temperature change

It requires heat to break the hydrogen bonds holding water together.

Large bodies of water absorb a lot of heat. Temperate climates Marine environment more stable than terrestrial Evaporative cooling

3. Unusual density properties

Ice is less dense than water, so ice floats! Allows aquatic life to survive in cold climates.

4. The universal solvent

Water can form hydrogen bonds with any polar or ionic compound.

Therefore, many things can be dissolved in water