Chemistry of Life

Biology Chapter 2

Elements

• Substances that cannot be broken down chemically into simpler kinds of matter

• More than 100 types• Organized on the

periodic table of elements

Elements of Life

• Approximately 27 are essential to life• 90% of mass of living things are O, C, H, N• Elements of Life: CHONPS• Remember the Elephants in the Element

Song?

Atom

• Smallest unit of an element that retains all the properties of that element

Nucleus

• Central region of an atom• Contains the bulk of the mass of the atom• Consists of protons and neutrons

Proton

• Positively charged particle• Located in Nucleus• Mass approximately 1 AMU

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Neutron

• Neutral charged particle, No Charge• Located in Nucleus• Mass approximately 1 AMU

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Electron

• Negatively charged particle• Orbits the nucleus in the electron cloud• Mass practically zero

Orbitals

• Electrons orbit in specific regions called orbitals-

• 3D space higher probability location of orbital• Each orbital is associated with an energy level• Electrons in orbitals further from the nucleus

have more energy

Electron Orbitals & Energy Levels

• Each orbital can hold 2 electrons• Each energy level consists of different #s of

orbitals

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Build an Atom

Atomic Number

• Number of protons in an atom • Determines type of element• Elements are organized by atomic number on

the periodic table• Atomic Number for Carbon is 6

Mass Number

• Total number of Protons + Neutrons

• Protons have mass of 1 amu

• Neutrons have mass of 1 amu

• Mass Number – Atomic Number = # of neutrons

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Mass Number

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Compounds

• Made of atoms of two or more elements in fixed proportions

• Chemical formula shows kinds and proportions of atoms

• H2O -

• C6H12O6 –

• CO2- • CO - • O2- Compound?

Molecule

• Simplest part of a substance that retains all properties of that substance

• Can exist in a free state• Can be very large- carbohydrates, lipids, proteins, nucleic

acids (macromolecules)• H2O -

• C6H12O6 –

• CO2- • CO - • O2-

Chemical Bonds

• Attractive forces that hold atoms together• Covalent Bonds• Ionic Bonds• Hydrogen Bonds

Stable Atom = Highest energy level filled

Valence Electrons

• Number of electrons in the highest energy level for that atom

• Atoms are more stable when outer energy level is full (2 or 8 electrons depending on element)

Dot Diagrams

• Show the valence electrons on an atom• Hydrogen and helium only hold up to 2

valence electrons• Other elements (that we will look at) hold up

to 8 valence electrons

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Covalent Bond

• Two atoms share one or more pairs of electrons

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Ion

• Some atoms only need to gain or lose 1 or 2 electrons to be stable

• Ions- Forms of an atom that have gained or lost electrons

• Fills the outer shell of electrons• If electrons are gained, Ion is NEGATIVE

(ANION)• If electrons are lost, Ion is POSITIVE (CATION)

Ion Example

• Sodium and Chlorine

Ionic Bonding

• Atoms form ions and become positive or negative

• Opposite charges attract