The Chemistry of Life Chapter 2

2.1 Start with Atoms Atoms are the smallest units of an element which still retain the unique properties of that element What are the basic components that make up an atom?

2.1 Start with Atoms The components of an atom are: –Protons (p + ) : Particles that have mass and carry a positive charge. –Neutrons (n): particles that carry mass but are not charged –Electrons (e - ): Particles that have little mass and carry a negative charge

Fig. 2.3, p. 22

2.1 Start with Atoms Each element has a unique atomic number, or the number of protons in the atom. –The atomic number is what conveys the unique properties of the atom or the element. –Example: Every atom with 8 protons is identified as an Oxygen atom. It behaves as oxygen due to the chemical characteristics bestowed upon it because of its 8 protons

2.1 Start with Atoms What would happen to an oxygen atom if we were to knock 2 protons out of its nucleus? Answer: it would turn into a carbon atom.

2.1 Start with Atoms Mass number is equal to the total number of protons and neutrons Example: Oxygen with 8 protons and 8 neutrons would have a mass number of 16.

Electrons An atom has about the same number of electrons as protons. Electrons which are negatively charged are effected by both the positive charged nucleus and the negative charge of other electrons.

Electrons Cont- How do negatively charged electrons spend as much time as possible near the nucleus and at the same time keep far enough away from other electrons? In order to stay as close to the positive charged nucleus as possible but away from each other, electrons travel different orbital paths or energy levels around the nucleus

Electrons For Example, the closest path near the nucleus is small. It can only hold two electrons before they start getting in each others way. HELIUM 2p+, 2e -

Electrons The Next orbital path is larger in circumference and is able to contain 8 electrons of higher energy. The carbon atom which has 6 electrons places 2 in the inner orbital and 4 in the outer.

Electrons Cont- Oxygen’s atomic number is 8. How would Oxygen’s electrons be represented around the nucleus?

Electrons Cont- Sodium has an atomic number of 11. How would sodium’s electrons be represented around the nucleus?

Electrons Cont- Chlorine has an atomic number of 17. How would Chorine's electrons be represented around the nucleus?

Electrons Bind Atoms together Atoms often are able to bind together to form molecules. –A molecule is a substance that has two or more atoms bound together. There are two different types of molecules –Elements are molecules that are made up of two or more atoms, but the atoms are all of the same type –Compounds are molecules that are made up of two or more different types of atoms

Molecules Question? – H2O is a A)Molecule B)compound C)Element D)A molecule and a Compound E)A molecule and an element F)A element and a molecule

Electrons Bind Atoms together The Rule of 8 –Atoms want to have a full outer shell of electrons –Atoms are very reactive to other atoms until they have a full outer orbital of electrons –Atoms will barrow or steal or give away electrons to other atoms to gain a complete orbital –In so doing they form bonds

Electrons Bind Atoms together There are three different types of bonds –Ionic bonds –Covalent bonds –Hydrogen bonds

SODIUM ATOM 11 p + 11 e - SODIUM ION 11 p + 10 e - electron transfer CHLORINE ATOM 17 p + 17 e - CHLORINE ION 17 p + 18 e - Fig. 2.10a, p. 26 Ionic Bonds

animation Click to view animation.

1 mm Fig. 2.10b, p. 26

Hydrogen bonding Hydrogen bonding is bonding that occurs between molecules not atoms Molecules that are made up of hydrogen atoms bonded to larger atoms have a polarity of charge. –One side of the molecule is positively charged and the other end is negatively charged

Hydrogen bonding Cont- The polarity of charge is due to the fact that electrons don’t spend as much time around the nucleus of hydrogen as they do around the nucleus of larger atoms. The hydrogen end of the molecule is positively charged while the opposite end is negatively charged slight negative charge at this end slight positive charge at this end O H H

O HH slight negative charge at this end slight positive charge at this end but the whole molecule has no net charge ( + and - balance each other) O H H O H H + _ _ + + Fig. 2.13, p. 28

Important Bonds in Biological Molecules Hydrogen bonds –Electronegative atom of a molecule weakly interacts with a hydrogen atom Hydrogen bonds may form between two or more molecules

Elements of life Carbon Hydrogen Nitrogen Oxygen Phosphorus Sulfur CHNOPS