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Atoms
Atoms
The study of chemistry begins with the basic unit of matter, the atom.
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Atoms
Placed side by side, 100 million atoms would make a row only about 1 centimeter long.
Atoms contain subatomic particles that are even smaller.
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Atoms
The subatomic particles that make up atoms are
protons
neutrons
electrons
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Atoms
The subatomic particles in a helium atom.
Helium atoms contain protons, neutrons, and electrons. The positively charged protons and uncharged neutrons are bound together in the dense nucleus, while the negatively charged electrons move in the space around the nucleus.
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Elements and Isotopes
Elements and Isotopes
A chemical element is a pure substance that consists entirely of one type of atom.
C stands for carbon.
Na stands for sodium.
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Elements and Isotopes
The number of protons in an atom of an element is the element's atomic number.
Commonly found in living organisms: C, H, O, N, P, S
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Atoms are Neutral
Atoms are neutral because they contain the same number of protons and electrons.
Carbon’s atomic number is 6.
How many protons are found in one atom of carbon?
How many electrons are found in one atom of carbon?
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Atomic Mass
Atomic Mass: the weighted average of all of an element’s naturally occurring isotopes
Usually NOT a whole number because it’s an average
We round this number to the nearest whole number to represent its mass number and determine the number of neutrons in an atom of an element.
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Neutrons
Mass Number: the total number of protons PLUS neutrons in the nucleus of an atom
We use the mass number to determine the number of neutrons in an atom.
For our purposes, we will round the atomic mass to the nearest whole number to represent the mass number of that isotope.
Mass Number – Atomic Number = # neutrons
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Elements and Isotopes
Isotopes
Atoms of the same element that differ in the number of neutrons they contain are known as isotopes.
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Elements and Isotopes
Because they have the same number of electrons, all isotopes of an element have the same chemical properties.
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Elements and Isotopes
Isotopes of Carbon
Because they have the same number of electrons, these isotopes of carbon have the same chemical properties. The difference among the isotopes is the number of neutrons in their nuclei.
6 electrons
6 protons
8 neutrons
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Elements and Isotopes
Radioactive Isotopes
Some isotopes are radioactive, meaning that their nuclei are unstable and break down at a constant rate over time
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Elements and Isotopes
Radioactive isotopes can be used:
to determine the ages of rocks and fossils.
to treat cancer.
to kill bacteria that cause food to spoil.
as labels or “tracers” to follow the movement of substances within an organism.
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15. Atomic Structure and Models
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Atomic Structure
Protons and neutrons form the nucleus.
The center of the atom
Where the mass is located
Electrons zoom around the nucleus in orbitals.
Electrons are organized in the following way:
first orbital: holds two electrons
second orbital: holds eight electrons
third orbital: holds eight electrons
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Valence Electrons
Valence electrons are the electrons located in the outermost orbital (valence orbital/shell) of an atom. The number of valence electrons of an atom determines its bonding patterns and chemical properties. We also use the valence electrons to draw the Lewis dot structure of an atom.
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Happy Atoms
Happy  atoms have either full or empty valence orbitals. Atoms form chemical bonds to make this happen…more on that later….
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Noble Gases
Elements located in the right-most column of the Periodic Table are called the Noble Gases. They have completely filled valence orbitals, so they DO NOT bond with other atoms…they are inert, or non-reactive.
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Bohr Model
Model of the atom most frequently used in science.
Determine the number of protons, neutrons, and electrons in the atom.
Draw the nucleus.
Place electrons into orbitals…do NOT pair until one parking space at each position is filled.
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Lewis Dot
This is a VERY easy way of representing the structure of an atom.
Write the chemical symbol. This represents the nucleus and all electrons EXCEPT the valence electrons.
Place the valence electrons around the symbol the same way you would place them in the outer orbital. DONE
Easy Peasy, Lemon Squeezy! 
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Chemical Compounds
Chemical Compounds
A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions.
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Chemical Compounds
Chemical Formula
Water
Table Salt
Hydrochloric Acid
Glucose
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Chemical Bonds
Chemical Bonds
The atoms in compounds are held together by chemical bonds.
The electrons that are available to form bonds are called valence electrons.
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Chemical Bonds
Ionic Bonds
An ionic bond is formed when one or more electrons are transferred from one atom to another.
These positively and negatively charged atoms are known as ions.
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Chemical Bonds
Sodium atom (Na)
Sodium ion (Cl-)
Sodium ion (Na+)
Sodium atom (Cl)
The chemical bond in which electrons are transferred from one atom to another is called an ionic bond. The compound sodium chloride forms when sodium loses its valence electron to chlorine.
Protons
Electrons
Charge
Protons
Electrons
Charge
Protons
Electrons
Charge
Protons
Electrons
Charge
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Chemical Bonds
Covalent Bonds
Sometimes electrons are shared by atoms instead of being transferred.
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Chemical Bonds
A covalent bond forms when electrons are shared between atoms.
single covalent bond
double bond
triple bond
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Chemical Bonds
The structure that results when atoms are joined together by covalent bonds is called a molecule.
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Chemical Bonds
Van der Waals Forces
When molecules are close together, a slight attraction can develop between the oppositely charged regions of nearby molecules.
van der Waals forces
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