Biology (Chapter 2: Essential Chemistry for Biology) Exam Class Notes v

(Chapter 2: Essential Chemistry for Biology) Exam Class Notes

Elements and Compounds

 Matter – Occupies space and has mass. Solid, liquid and gas (also plasma).

 Mass – amount of material. Is not equivalent to weight.

 Element – basic unit of matter. Cannot be broken down into parts that are considered

matter. There are 92 natural elements (and some artificially created).

 In the periodic table each element is represented by a symbol along with atomic number

and atomic mass.

 25 elements are essential to people (and animals). This was tested by dividing them of an

element.

 Carbon, Nitrogen, Oxygen, and Hydrogen make up 96% of our body. Most of the rest of

the 4% are elements needed in small amounts. Iron for hemoglobin, calcium for bones,

phosphorus for the sugar-phosphate backbone of DNA. Trace elements are needed in

very small amounts.

 2 or more elements combine to form compounds.

 Elements are made of atoms. Atoms are the smallest unit of matter. Atoms are made of

protons with positive charge in nucleus. Electrons with negative charge surrounding the

nucleus. Neutrons with no charge in nucleus.

 If # protons = # electrons, the atom will be neutral.

 All atoms of an element have the same number of protons, but they may have a different

number of electrons = ions, or a different number of neutrons = isotope.

 The atomic number is number of protons.

 Atomic mass = # proton + # neutrons. (Electrons weigh very little).