2 Chemistry Review
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Transcript of 2 Chemistry Review
![Page 1: 2 Chemistry Review](https://reader035.fdocuments.us/reader035/viewer/2022062410/5695d0941a28ab9b02930a59/html5/thumbnails/1.jpg)
Chemistry Review
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Chapter Outline
• What are atoms?
• How do atoms interact to form molecules?
• Why is water so important to life?
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What are Atoms?
• All matter is composed of very small particles called atoms
• Atoms themselves are composed of smaller, subatomic particles called protons, neutrons and electrons
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What are Atoms?
Name of
Particle
Location of
Particles
Charge of
Particle
Mass of
Particle
Proton Nucleus Positive 1 amu
Neutron Nucleus Neutral 1 amu
Electron Orbits around nucleus
Negative 1/2000 amu
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What are Atoms?
• Bohr Model of the Sodium Atom
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What are Atoms?
• There are approximately 100 different types of atoms
• These correspond to the 100 elements present on the Periodic Table of the Elements
• Elements on the Periodic Table are organized by atomic number, atomic mass, and similar properties
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What are Atoms?
• Atomic Number =
# of protons =
# of electrons
Atomic Mass =
# of protons +
# of neutrons
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What are Atoms?
• Using the Periodic Table
• # protons= atomic number
• # electrons= atomic number
• # neutrons= atomic mass – atomic number
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What are Atoms?
• The protons and neutrons are in the central nucleus
• Electrons arrange themselves into distinct orbitals around the nucleus
• The first orbital nearest the nucleus holds a maximum of 2 electrons
• The remaining outer orbitals hold a maximum of 8 electrons each
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• For example, sodium is atomic number 11 and atomic mass 23
• #protons= 11
• #electrons= 11
• #neutrons= 23-11 = 12
• The sodium atom has 11 electrons: 2, 8 and 1 electron in the outer orbital
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What are Atoms?
• For example, chlorine is atomic number 17 and atomic mass 35
• #protons= 17
• #electrons= 17
• #neutrons= 35 – 17 = 18
• The chlorine atom has 17 electrons: 2, 8, and 7 electrons in the outer orbital
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How do atoms interact to form molecules?
• The Octet Rule states that atoms are most stable if the outer orbital is either full (8 electrons) or empty (0 electrons)
• Atoms will lose or gain electrons in order to fill the orbital and achieve stability
• When atoms lose or gain electrons, they become charged atoms called ions
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How do atoms interact to form molecules?
• For example, sodium has one outer electron and will lose the one electron in order to become stable → +1 sodium ion
• For example, chlorine has seven outer electrons and will gain one electron in order to become stable → -1 chlorine ion
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How do atoms interact to form molecules?
• Ions of opposite charge attract to form ionic compounds
• +1 Na ion + -1 Cl ion → NaCl compound
• The bond that keeps the ions together is called an ionic bond
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What are Atoms?
• Outer orbitals of Na and Cl ions
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How do atoms interact to form molecules?
• Metallic and non-metallic elements on the periodic table form ionic compounds by losing/gaining electrons
• Non-metallic and non-metallic elements form covalent compounds by sharing electrons
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How do atoms interact to form molecules?
• For example, H atom has one outer electron: it needs one more electron to become stable
• C atom has four outer electrons: it needs four more electrons to become stable
• Four H atoms will share their electrons with one C atom so the C atom will be stable
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How do atoms interact to form molecules?
• One C atom will share its four electrons with four H atoms in order for the H atoms to become stable
• The bond that forms between the atoms is called a covalent bond: the equal sharing of electrons between atoms
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How do atoms interact to form molecules?
• Outer orbitals of H and C atoms
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How do atoms interact to form molecules?
• Non-metallic and non-metallic atoms do not always share their electrons equally
• For example, H and O are non-metallic elements
• When H and O atoms share electrons, the O atom has a stronger pull on the H atom’s electrons → the O atom becomes slightly negative, the H atom slightly positive
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How do atoms interact to form molecules?
• This unequal sharing of electrons creates a polar covalent bond between H and O atoms
• The molecule as a whole has no net charge, but there are distinct poles of charge
• The molecule is a polar covalent compound
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Why is water so important to life?
• Water is a polar covalent molecule held together by polar covalent bonds between H and O atoms
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Why is water so important to life?
• Because water is a polar covalent molecule, the slightly positive H regions of one water molecule will attract the slightly negative O regions of another water molecule
• This electrical attraction between the water molecules is called hydrogen bonding
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Why is water so important to life?
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Why is water so important to life?
• The extraordinary properties of water are due to water’s intramolecular polar covalent bonds and intermolecular hydrogen bonds
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Why is water so important to life?
• Water is a good solvent: it interacts with many other molecules that are ionic or polar covalent
• Water molecules are cohesive (stick together) due to hydrogen bonding between water molecules
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Why is water so important to life?
• Because of hydrogen bonding between water molecules, it takes a large amount of added energy to change water from solid→liquid→gas (energy of vaporization)
• Because of hydrogen bonding between water molecules, one must remove a large amount of energy in order to change water from gas→liquid→solid (energy of fusion)
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Why is water so important to life?
• Water can dissociate (separate) into +1 H atoms and -1 OH ions in a solution
• The amount of +1 H ions vary within and between biological and chemical systems
• Systems that have an excess of +1 H ions are described as acidic
• Systems that have an excess of -1 OH ions are described as basic
• Systems that have equal amounts of +1 H ions and -1 OH ions are described as neutral
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Why is water so important to life?
• The pH scale measures the degree of acidity/ alkalinity in a system
• Acidic < pH 7
• Neutral = pH 7
• Basic > pH 7
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• A chemical that ends to maintain a solution at a constant pH is called a buffer
• When the solution becomes too basic, buffers release +1 H ions into the solution to decrease pH
• When the solution becomes too acidic, buffers collect and remove +1 H ions from the solution in order to increase pH