Introduction to Chemistry

Objectives…

• Define chemical element, atom, ion, molecule and compound

• Explain how chemical bonds form• Describe what happens in a

chemical reaction and explain why it is important to the human body

Chemical Element

• Substances that cannot be broken down by normal chemical means

• ~112 known chemical elements• Each is designated by a chemical

symbol

• 26 elements are found in the human body

• 96% of the body’s mass is made from Carbon, Hydrogen, Oxygen and Nitrogen

• 3.8% is from Calcium, phosphorus, potassium, sulfur, sodium, chlorine, magnesium and iorn

Trace Elements

• The remaining 0.2% of the body’s mass is made of these 14 elements:– Al, B, Cr, Co, Cu, F, I, Mn, Mo, Se, Si,

Sn, V and Zn– Even though they are present in

REALLY small amounts, they are still essential to maintain homeostasis!

Atoms

• Each element is made up of a single type of atom

• The are the smallest units of matter that retain the properties of the element

Subatomic Particles• Protons (+) and Neutrons (0) are

located in the nucleus of the atom• Electrons (-) move around in the

space surrounding the nucleus

• The number of protons in an atom equals the number of electrons, giving the atom a net charge of zero

• Atomic Number – the number of protons

• Atomic Mass – the number of protons plus the number of neutrons

• Electron Shells – the area around a nucleus where you are most likely to find an electron

Ions

• If an atom gives up or gains an electron it becomes an ion.

• An ion is an atom that has a positive or negative charge due to unequal numbers of protons and electrons

• Cation – a positive ion• Anion – a negative ion

Molecules

• When 2 or more atoms share electrons, the resulting combination is called a molecule

• May be 2 or more atoms of the same element (O2) or of different elements (H2O).

Molecular Formulas

• A molecular formula indicates the type of and how many atoms are in a molecule– Ex – H2O means 2 hydrogen atoms

and 1 oxygen atoms have joined

Compound

• A molecule containing 2 or more atoms of different elements

Free Radical

• An electrically charged ion or molecule that has an unpaired electron in its outermost shell

• A free radical is unstable and destructive to nearby molecules

• They break apart other molecules in the body by either giving up their unpaired electron or by taking an electron from another molecule.

Free Radicals in your Body…

• Many processes in the body generate free radicals

• Diseases associated with oxygen derived free radicals are cancer, artherosclerosis, Alzheimers, emphysema, diabetes, cataracts, macular degeneration, rheumatoid arthritis, and deterioration associated with aging.

Antioxidants

• Substances that inactivate oxygen associated free radicals.

• Consumption of antioxidants is though to slow the pace of damage caused by free radicals.

• Dietary sources of antioxidants include selenium, beta-carotene and vitamins C and E. “The antioxidant will protect me…”

Chemical Bonds• Forces that bind the atoms of molecules

together, resisting their separation.• Given the right conditions, two or more

atoms can interact (bond) in such a way that a chemically stable arrangement of 8 valence (outer) electrons in each atom

• 3 types of bonds:– Ionic– Covalent– Hydrogen (not really a bond if you talk to a

chemist, but a REALLY strong attraction)

Ionic Bonds

• The force of attraction between ions of opposite charges

• This results from the transfer of electrons

• Ionic bonds are found mainly in teeth and bones, most other ions in the body are dissolved in fluid.

Electrolytes

• An ionic compound that breaks apart into cations and anions when dissolved is called an electrolyte because the resulting solution can conduct an electric current

• Critical in controlling water movement, maintaining acid/base balance and producing nerve impulses

Covalent Bonds

• Atoms form a molecule by sharing one, two or three pairs of electrons

• These are the most common chemical bonds in the body

Polarity

• If the neither atom in a covalent molecule has a greater attraction for electrons than the other the bond is said to be non-polar

• Sometimes the electrons are not shared equally – one atom attracts the electrons more strongly than the other. This results in a polar bond

Polar Covalent Bonds

• The sharing of electrons is unequal• The side of the molecule that attracts

more electrons will have a partial negative charge (-) while the side that does not have as many electrons will have a partial positive charge (+)

• The ENTIRE molecule is still NEUTRAL

Hydrogen Bonds

• A VERY VERY strong interaction between some polar molecules containing hydrogen

• A hydrogen atom in one molecule with a partial positive charge attracts a partial negative atom (F, O or N) from another molecule.

• About 5% as strong as an actual covalent bond

Chemical Reactions

• New bonds form and old bond are broken

Chemical Energy

• Form of potential energy stored in chemical bonds

• Breaking old bonds requires the input of energy, forming new bonds releases energy

Synthesis Reactions

• Smaller molecules join to make larger molecules

Decomposition Reaction

• Larger molecules are broken down into smaller molecules

Exchange Reactions

• Consist of both synthesis and decomposition

AB + CD AD + BC

Reversible Reactions

• Reactions that can proceed in either direction

AB A + B