The �Basics of Biology Notes

Wait, why are we studying chemistry?

Chemistry is the foundation of Biology. Life is not only made up of chemical elements but chemical reactions.

Objective 1: Describe how chemical reactions cause change in molecules.�What is an atom?�

• An atom is the smallest part of an element that keeps all the properties of the element.
• CHNOPS: elements essential for life
• Carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur

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• -Electron = Negative charge=SAME AS atomic number
• -Proton = + charge=SAME AS atomic number
• -Neutron (Neutrally charged) = Mass-number

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Life requires ~25 chemical elements

• About 25 elements are essential for life
• Four elements make up 96% of living matter:

• carbon (C) • hydrogen (H)

• oxygen (O) • nitrogen (N)

• Four elements make up most of remaining 4%:

• phosphorus (P) • calcium (Ca)

• sulfur (S) • potassium (K)

Proton

Neutron

Electron

Hydrogen

1 proton

1 electron

Oxygen

8 protons

8 neutrons

8 electrons

+

0

–

• Everything is made of matter
• Matter is made of atoms

What is an element?�

• -An element is made up of only one kind of atom. An element can’t be broken down into a simpler form by chemical reactions. Elements are arranged in a chart known as the periodic table. The table tells us it’s mass, how many protons it has, and its symbol.
• Trace elements:  are those required by an organism in minute quantities.

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• -A compound is made up of two or more elements in exact proportions. There are two types of compounds ionic and molecular. Ionic compounds attract one to one another to form a neutral compound such as salt NaCl.

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The World of Elements

C

Different kinds of atoms = elements

H

O

N

P

S

Na

K

Mg

Ca

-What is a Molecule?�

• -A molecule is a group of atoms held together by the energy of chemical bonds.

-----Energy is the capacity to cause change.

-----Potential energy is the energy that matter has because of its location or structure. The electrons of an atom differ in their amounts of potential energy. An electron’s state of potential energy is called its energy level, or electron shell.

• All compounds are molecules but not all molecules are compounds. Molecules can bind to the same element or a different element. Compounds are two or more different elements bonded together.

• Its all about the electrons
• electrons determine chemical behavior of atom
• depends on number�of electrons in atom’s outermost shell
• Known as the valence shell
• Electrons will try to empty or fill up the valence shell by sharing/giving/taking electrons from other atoms.

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How electrons bond atoms together

How does this �atom behave?

• Effect of electrons
• chemical behavior of an atom depends on number of electrons in its valence shell

What’s the�magic number?

How does this atom behave?

How does this atom behave?

How electrons bond atoms together

Elements & their valence shells

Elements in the same row have the same number of shells

Moving from left to right, each element has a sequential addition of electrons (& protons)

Elements & their valence shells

Elements in the same column have the same valence & similar chemical properties

Remember

some food chains�are built on � reducing O to H₂O

& some on

reducing S to H₂S

• Atoms tend to
• complete a partially filled valence shell

or

• empty a partially filled valence shell

This tendency drives chemical reactions…

and creates bonds

How electrons bond atoms together

Bonds in Biology

• Weak bonds
• hydrogen bonds
• attraction between + and – area of two molecules (Example: water-water)
• Ionic Bonds: an atom with a + charge is attracted to an atom with a negative charge. Example: NaCl.
• Strong bonds
• covalent bonds are formed

when electrons are shared

between atoms

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Ionic bond

Hydrogen bond

H₂O

H₂O

Hydrogen bonding

• Polar water creates molecular attractions
• attraction between positive H in one H₂O molecule to negative O in another H₂O
• also can occur wherever �an -OH exists in a larger �molecule
• Weak bond

Let’s go to the �videotape!

H

O

H

Covalent bonds

• Why are covalent bonds strong bonds?
• two atoms share a pair of electrons
• both atoms holding onto the electrons
• very stable
• Forms molecules

H₂ (hydrogen gas)

H — H

H₂O (water)

Reactions

• Chemical reaction: process by which substances change into different substances through the breaking and forming of chemical bonds.
• Reactant: substance that is changed by a chemical reaction.
• Product: substance formed by a chemical reaction.

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Hydrogen gas +_Oxygen gas forms 2 water molecules. The Hydrogen and oxygen gasses are reactants. The 2 water molecules are the products.

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• Equilibrium: condition in which reactants and products of a chemical reaction are formed at the same rate.

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• Exothermic: chemical reaction that yields a net release of energy in the form of heat. Think…. fire, sound, or light released.

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• Endothermic: chemical reaction that requires a net input of energy. Think ice cream cone melting because it is absorbing heat from the surroundings.

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2H₂ + O₂ 2H₂O

Subscripts and Coefficients�Atoms vs Molecules

• Subscript - shows how many atoms of an element are in a molecule.
• EX: H₂O
• 2 atoms of hydrogen (H)‏
• 1 atom of oxygen (O)‏
• Coefficient - shows how many molecules there are of a particular chemical.
• EX: 3 H₂O
• Means there are 3 water molecules.