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Chapter 2 Of Atoms and Molecules: Chemistry Basics

Chapter 2 Of Atoms and Molecules: Chemistry Basics

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A. Matter Material that takes up space. Matter broken down to pure substances- Elements 1. Elements Pure chemical substances composed of atoms. Examples? Oxygen, sodium, copper, potassium How many elements exist? (92)

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Page 1: Chapter 2 Of Atoms and Molecules: Chemistry Basics

Chapter 2

Of Atoms and Molecules: Chemistry Basics

Page 2: Chapter 2 Of Atoms and Molecules: Chemistry Basics

All organisms consist of matter and energy.

LIFE- based on chemical principles.

MATTER – The basis for everything

Page 3: Chapter 2 Of Atoms and Molecules: Chemistry Basics

A. MatterMaterial that takes up space. Matter

broken down to pure substances- Elements

1. ElementsPure chemical substances

composed of atoms.• Examples?

• Oxygen, sodium, copper, potassium• How many elements exist? (92)

Page 4: Chapter 2 Of Atoms and Molecules: Chemistry Basics

• How many of these elements are essential to life? (25)• The essential elements are divided

into:• Bulk elements: needed in

relatively large amounts• Examples: C, O, H, N

• Trace elements: needed in relatively small amounts• Examples: Fe, K, Na, Zn, Ca

Page 5: Chapter 2 Of Atoms and Molecules: Chemistry Basics

Periodic Table of Elements

Page 6: Chapter 2 Of Atoms and Molecules: Chemistry Basics
Page 7: Chapter 2 Of Atoms and Molecules: Chemistry Basics

2. AtomThe smallest “piece” of an element

that retains the characteristics of that element.

Composed of 3 subatomic particles:• Protons• Neutrons• Electrons

Page 8: Chapter 2 Of Atoms and Molecules: Chemistry Basics

Atoms of each element – characteristic number of protons# of protons – determines size and character of each atom.Charge- attraction between opposite types of particles.Atom – electrically neutralElectron – small compared to proton and neutronOrbital- location for an electron relative to its nucleus.

Page 9: Chapter 2 Of Atoms and Molecules: Chemistry Basics

Element – has a symbol.He- HeliumNa- SodiumAtomic number- shows the # protons in the atom- identity of the atom.Elements are arranged sequentially in the periodic table by atomic number.

Page 10: Chapter 2 Of Atoms and Molecules: Chemistry Basics

Characteristics of Subatomic Particles

Page 11: Chapter 2 Of Atoms and Molecules: Chemistry Basics

Atomic number• # protons in nucleus of an atom

(establishes identity of the atom)• Since most atoms are electrically

neutral, atomic number indicates # of electrons as well.

Atomic mass• # protons plus # neutrons in

nucleus of an atom

Page 12: Chapter 2 Of Atoms and Molecules: Chemistry Basics

Periodic table information on carbon:

Atomic mass given in table is average mass of all the element’s isotopes.

Page 13: Chapter 2 Of Atoms and Molecules: Chemistry Basics

How can we determine the number of neutrons in an atom?• # neutrons = atomic mass - atomic #

• Determine # neutrons in a carbon atom (atomic mass = 12; atomic # = 6).• # neutrons = 12 - 6 = 6

Do all carbon atoms have the same number of protons?

Do all carbon atoms have the same number of neutrons?

Page 14: Chapter 2 Of Atoms and Molecules: Chemistry Basics

Isotopes• Atoms having the same number of

protons, but differing numbers of neutrons.

• Same charge & characteristics but different masses.

• Often one isotope is very abundant and others are rare.

• If an isotope is unstable, it is termed radioactive

Ex. Carbon isotopes• carbon 12 (12C) 6 neutrons• carbon 13 (13C) 7 neutrons• carbon 14 (14C) 8 neutrons

Page 15: Chapter 2 Of Atoms and Molecules: Chemistry Basics

3. CompoundA pure substance formed when atoms of

different elements bond.The number of atoms of each element is

written as a subscript.Examples:• CO2 carbon dioxide• H2O water• CH4 methane• C6H12O6 glucose

Atoms bound together – molecules

Page 16: Chapter 2 Of Atoms and Molecules: Chemistry Basics

4. MoleculeSmallest piece of a compound that

retains characteristics of that compound.

The number of molecules is written as a coefficient.

Examples:• 4CO2 4 molecules of carbon dioxide• 2C6H12O6 2 molecules of glucose• 6O2 6 molecules of oxygen

Page 17: Chapter 2 Of Atoms and Molecules: Chemistry Basics

Chemical Reactions• The reactants of a reaction are

written to the left of the arrow.• The products of a reaction are

written to the right of the arrow.

Example:6O2 + C6H12O6 6H2O + 6CO2 + energy

Page 18: Chapter 2 Of Atoms and Molecules: Chemistry Basics

5. Chemical Bonds• Type of bond formed is determined by the number of valence electrons in the interacting atoms [octet rule].

• The goal of chemical bonding is for all atoms involved to complete or eliminate their outer electron shells.

Page 19: Chapter 2 Of Atoms and Molecules: Chemistry Basics
Page 20: Chapter 2 Of Atoms and Molecules: Chemistry Basics

a) Covalent bonds - form when atoms share electron pairs.• strongest type of bond• tend to form when atoms have 3,

4 or 5 valence electrons• the number of electron pairs

shared determines whether the covalent bond is single, double or triple

• can be nonpolar or polar

Page 21: Chapter 2 Of Atoms and Molecules: Chemistry Basics
Page 22: Chapter 2 Of Atoms and Molecules: Chemistry Basics

Nonpolar covalent bonds - electrons are shared equally between atoms.

Ex. methane

Page 23: Chapter 2 Of Atoms and Molecules: Chemistry Basics

Types of diagrams to represent molecules

Page 24: Chapter 2 Of Atoms and Molecules: Chemistry Basics

Polar covalent bonds - electrons are not shared equally. They are drawn more strongly to 1 atom’s nucleus than the other.

Form when less electronegative atoms bond with more highly electronegative atoms.

Ex. water

Page 25: Chapter 2 Of Atoms and Molecules: Chemistry Basics

b) Ionic bonds - form when oppositely charged ions are attracted to each other. • weaker than covalent bonds • atoms with 1, 2 or 3 valence electrons

give up electrons to atoms with 7, 6 or 5 valence electrons which forms ions

• form salts which break apart in waterEx. NaCl

Page 26: Chapter 2 Of Atoms and Molecules: Chemistry Basics

c) Hydrogen bonds - form when opposite charges on two molecules are attracted to each other.• weakest type of bond*

Ex. DNA H2O

Page 27: Chapter 2 Of Atoms and Molecules: Chemistry Basics

6. Attractive forces• van der Waals attraction• Attraction between molecules

or within molecules that occur when oppositely charged regions approach each other

• Often used to shape molecules

Page 28: Chapter 2 Of Atoms and Molecules: Chemistry Basics

• Interactions with waterhydrophobic: parts of a

molecule that do not have charges cannot interact with water

hydrophilic: parts of a molecule that have charges can interact with water

Page 29: Chapter 2 Of Atoms and Molecules: Chemistry Basics

B. The Importance of Water1. Properties• Cohesion - the attraction of water

molecules for each other.• Adhesion - the attraction of water

molecules for other compounds.• Imbibition – the tendency to absorb

water and swell

Page 30: Chapter 2 Of Atoms and Molecules: Chemistry Basics

• High heat capacity – takes a great deal of heat to raise the temperature of water.

• High heat of vaporization - a lot of heat is required to evaporate water.

• Exists as solid, liquid or gas - solid (ice) is less dense than liquid.

Page 31: Chapter 2 Of Atoms and Molecules: Chemistry Basics

2. SolutionsA solution is a mixture of one or more solutes dissolved in a solvent.

If solvent is water, then it is an aqueous solution.

Water is a strong solvent because it separates charged atoms or molecules.

Page 32: Chapter 2 Of Atoms and Molecules: Chemistry Basics

3. Acids & Bases• Acids - substances

that add H+ to a solution.

• Bases - substances that remove H+ from solution.

• Buffer systems: help stabilize pH

pH scale is measure of acidity/alkalinity based on H+ concentration.