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Chemistry in BiologyChapter 6
What do you know about atoms?
KWL Chart
The smallest unit of matter The building blocks of matter
Atoms
Atoms are so small that billions of them fit on the head of a pin
Atoms are made up of protons, neutrons, and electrons◦ Protons and neutrons are located at the center of the
atom, called the atomic nucleus Protons
◦ Positively charged particles Neutrons
◦ Particles that have no charge Electrons
◦ Negatively charged particles
Structure of Atoms
Located outside of the nucleus Constantly move around the nucleus at
different energy levels The basic structure of an atom is the result
of the attraction between protons and electrons
Electrons
Let’s create a concept map comparing and contrasting electrons, neutrons, and protons
Concept Map
Protons
Electrons
NeutronsPositively charged No charge
Negatively charged
Make up the atomic nucleus
In even amounts of elements
Weigh the same
Rotate around atomic nucleus or outsideWeigh an 1/1800 of a proton
Make up an atom
An element is a pure substance that cannot be broken down into other substances
Made up of only one type of atom
There are over 100 known elements, and 92 of these occur in nature
Elements
Organized into horizontal rows called Periods
Organized into vertical columns called Groups
Each individual block represents an element
The Periodic Table of Elements
Atoms of the same element that have different numbers of neutrons
Isotopes
Changing the number of neutrons can affect the stability of the nucleus and in some cases causing the nucleus to decay, or break apart
In some cases, it gives off radiation The radiation can be detected and used for
many applications Example: Carbon Dating (carbon-14) to
calculate the age of an object
Radioactive Isotopes
A compound is a pure substance formed when two or more different elements combine
Example: NaCl (Sodium Chloride), H2O (Water)
Compounds
Always formed with a specific combination of elements in a fixed ratio◦ Ex: Water is always formed in a ratio of two
hydrogen and one oxygen◦ Each water molecule has the same structure
Chemically and physically different than the elements that comprise them◦ Ex: Water has different properties than hydrogen
or oxygen
Unique Characteristics
Cannot be broken down into simpler means, such as tearing or crushing◦ Can be broken down by chemical means into
simpler compounds or into their original elements
Unique Characteristics
Draw the chemical structure of:◦ H2O
◦ CO2
◦ NaCl◦ CO
In Your Notes:
The force that holds the substances together
The nucleus determines the chemical identity of an atom
The electrons are involved directly in forming chemical bonds
Chemical Bonds
Electrons travel around the nucleus of an atom in areas called energy levels
Each energy level has a specific number of electrons that it can hold at any time
The first can hold up to 2 electrons The second can hold up to 8 electrons
How Bonding Works
A partially-filled energy level is not stable Atoms become more stable by losing
electrons or attracting electrons from other atoms
This results in the chemical formation of chemical bonds between atoms
This forming of bonds stores energy (absorb) and the breaking of bonds provides energy (release) for growth, development, adaptation, and reproduction in living things
Forms when electrons are shared◦ Ex: H2O
Most compounds in living organisms have covalent bonds holding them together
A molecule is a compound in which the atoms are held together by covalent bonds◦ Ex: H2O◦ Depending on the number of shared electrons,
covalent bonds can be single, double, or triple
Covalent Bonds
Electrical attraction between two oppositely charged atoms or groups of atoms called ions
Ions are atoms that have lost or gained one or more electrons and carries an electric charge◦ Ex:Na+, Cl-
Ionic Bonds
Remember: Atoms are neutral In order for an atom to be most stable, the
outermost energy level should either be completely filled or empty.
Some atoms tend to give up (donate) or obtain (accept) electrons to empty or fill the outer energy levels in order to be stable.◦ This leads to atoms with a charge
How Ionic Bonds Work
Substances formed by ionic bonds are called ionic compounds
Ions in living things include Sodium, Potassium, Calcium, Chloride, and Carbonate ions
They help to maintain homeostasis as they travel in and out of the cells
They help transmit signals among cells that allow you to see, taste, hear, feel, and smell
Ionic Bonds
Draw your own covalent and ionic bonds on the whiteboards◦ Covalent: show electrons shared◦ Ionic: show electrons that are distributed
unequally Practice with these: NaCl, H2O, H2, O2, N2,
KCl, NaBr
Try it on your own!
Covalent Bonds
Low Polarity
Formed between two non-metals
Share electrons
Definite Shape
Examples: CH4 and HCl
Ionic Bonds
High Polarity
Formed between a metal and non-metal
Non-metals are stronger than metal and can get electrons easily
No definite shape
Examples: NaCl, H2SO4
Similarities and Differences
Positive ions and negative ions form based on the ability of an atom to attract electrons
If the nucleus of the atom has a weak attraction for the electron it will donate the electron to an atom with a stronger attraction
Elements in covalent bonds do not always attract electrons equally
Review
Electrons in a molecule are in random motion around the nuclei. This causes an unequal distribution of the electron cloud around the molecule creating temporary areas of lightly positive and negative charges
Review
When molecules come close together, the attractive forces between these positive and negative regions pull on the molecules and hold them together
The strength of the attraction depends on the size of the molecule, its shape, and its ability to attract electrons
Not as strong as covalent and ionic bonds Ex: Allow water droplets to form
Van der Waals Forces