1. Chapter 1: Chemical Bonds
Chemistry
Chapter 1: Chemical Bonds

2. Vocab Electron cloud Energy levels Periodic Table Electron dot diagram
Chemical bond

3. Atom Structure Everything is made up of atoms
At the center of every atom is a nucleus containing protons (+ charge) and neutrons (no charge)
The nucleus represents most of the atom’s space
The rest of the atom’s space is empty except for the atom’s electrons (- charge) which travel in an area of space around the nucleus called the electron cloud

6. Electrons Electrons have negative charges
Electrons travel in predictable areas (electron clouds) but not predictable patterns

7. Element Structure
Each element has a different atomic structure made up of a specific number of protons, electrons, and neutrons
The number of protons and electrons is always the same for a neutral element

8. Electron Arrangement
The number and arrangement of electrons in the electron cloud are responsible for many of the chemical and physical properties of that element.

9. Electron Energy
All electrons in an atom are in the electron cloud but some electrons are closer to the nucleus than others
Energy levels: The different positions of electrons in an atom
Each level represents a different amount of energy

10. Number of Electrons
Each energy level can hold a specific number of electrons
The farther away an energy level is from the nucleus the more electrons it can hold
Ex. The first can hold 2, the second up to 8, and the third up to 18 electrons

11. Second Energy Level
First Energy Level

12. Energy Steps
A stairway is an excellent model to show the maximum number of electrons each energy level can hold in the electron cloud.
Electrons nearest the nucleus have the lowest amounts of energy and are the hardest to remove
Electrons farthest from the nucleus have the most amounts of energy and are the easiest to remove

13. Energy Steps

14. Ex. Picture a magnet with a chain of paperclips hanging off of it.
The easiest paperclip to remove is the one at the very end of the chain because the pull of the magnet isn’t as strong
Hardest to remove
Easiest to remove

15. Periodic Table and Energy Levels
Periodic Table: A way of representing all of the elements in a way that shows their similarities and differences
First discovered by Dmitri Mendeleev in 1869
Horizontal rows are called periods
Vertical columns are called groups or families
The atomic number is the same as
the number of protons and electrons
Today’s periodic table is still based on the one I created almost 140 years ago!

16. Reading the Periodic Table

20. Electron Configuration
The number of electrons in a neutral atom increases from left to right across a period
Atoms whose outer energy levels contain one of the levels in the stair step analogy are considered stable
Each period ends with a stable element

21. Element Families Each column of the Periodic Table contains one family
Hydrogen is considered separate from the rest of the families
Just like human families, element families have similar traits (chemical properties)
Mendeleev was inspired by the repeating patterns he heard in music and saw similar repeating patterns in the elements

22. Noble Gases Made up of the elements in Group 18
Helium, Neon, Argon, Krypton, Xenon, Radon
All are stable and have 8 electrons in their outer energy levels
At one time these gases were thought to be inert (non reactive) but this was later found to be untrue and the name changed to the Noble gases
Used to protect filaments in light bulbs and produce colored light in signs

23. Halogens Made up of the elements in Group 17
Fluorine, Chlorine, Bromine, Iodine, Astatine
Unstable – Halogens need one electron to obtain a stable outer energy level
The easier it is for a Halogen to form a bond, the more reactive it is
Fluorine is the most reactive because its outer energy level is closest to the nucleus
Used to disinfect drinking water, in clothing bleach, production of paper, and removal of germs during sterilization

24. Alkali Metals Made up of the elements in Group 1
Lithium, Sodium, Potassium, Rubidium, Caesium, Francium (Hydrogen is not included)
Unstable - have one electron in their outer energy level  Highly reactive
Used to create flavorings and preservatives and in the manufacturing of paper, soap, and ceramics

26. Electron Dot Diagrams
Electron dot diagram: a diagram that shows the number of electrons in the outer energy level
Valance Electrons: electrons in the outer energy level
Helpful in determining the chemical properties of an atom and when showing how atoms bond
Also called Lewis Structures
Created by Gilbert N. Lewis

27. How to Write Them
For groups 1, 2 and see pg. 11 in your book.
Dots are written in pairs on the four sides of the element symbol
The dots are written in this order 1 5 Ne 4 6 8 2 3 7

28. Using Dot Diagrams Can be used to show how atoms bond with each other
Chemical Bond: the force that holds two atoms together
Atoms bond with each other in a way that makes them become more stable by filling up their outer energy levels

29. Section 2: How Elements Bond

30. Vocab Ion Ionic bond Compound Covalent bond Metallic bond Molecule
Polar bond
Chemical formula

31. How Elements Bond
When atoms are joined together they do not fall apart easily
Atoms form bonds with other atoms using the electrons in their outer energy level
There are 4 ways this can be done:
Losing electrons
Gaining electrons
Pooling electrons
Sharing electrons

32. Ionic Bonds – Loss and Gain
Occurs between metals and nonmetals
Atoms gain and lose electrons to form bonds

33. Ions – A Question of Balance
Atoms lose or gain electrons and become more stable
When an electron is lost, the electric charge changes because there is now one more proton than neutron in the nucleus and it is called a positive ion
When an electron is gained you create a negative ion
Ion: an atom that is no longer neutral because it has lost or gained an electron

34. Examples of ions: Sodium loses one electron to become a Na+ ion
Chlorine gains one electron to become a Cl- ion

36. Bond Formation
Negatively charged ions and positively charged ions are attracted to each other
Ionic Bond: attraction that holds oppositely charged ions together
Ex. Sodium (Na) loses an electron and becomes a positive ion. Chlorine (Cl) gains an electron from Sodium (Na) and becomes a negative ion.
The two ions are attracted together by an ionic bond

39. Pure substances are divided into two categories:
Element: cannot be separated into any simpler substances
Ex. Sodium and Chlorine
Compound: a substance containing two or more elements that are chemically bonded
Ex. Sodium Chloride

40. More Gains and Loses
Some atoms need to lose/gain more than two electrons to become stable
Atoms can do this by bonding to another atom that needs to gain/lose as many electrons as they need to lose/gain or by bonding to more than 1 atom

41. Ex: Magnesium needs to lose 2 electrons
Oxygen needs to gain 2 electrons
The 2 in the superscript represents the number of electrons that were gained/lost
If only one electron is gained or lost no number is needed in the superscript

42. Ex: Magnesium needs to lose 2 electrons
2 Chlorine atoms that each need to gain 1 electron

43. Metallic Bonding - Pooling
Occurs between two metals
Metallic Bonding: Metal atoms pool their electrons to form bonds
In metals, electrons are not held tightly to the individual atoms. Instead they move freely among all the atoms in the metal forming a shared pool of electrons
This is why metal can be hammered into sheets without breaking and is a good conductor of electricity

45. Covalent Bonds - Sharing
Occurs between 2 nonmetals
Some atoms need to gain/lose too many electrons (this needs too much energy) to create ionic bonds
Instead two nonmetals share their electrons
Covalent Bond: chemical bond that forms between the shared electrons
Electrons are attracted to the nuclei of both atoms and move back and forth between them
Molecule: neutral particle formed in a covalent bond

46. Ex.
Two chlorine atoms form a stable molecule by sharing electrons to fill their outer energy level

47. Double and Triple Bonds
Sometimes an atom shares more than one electron with another atom
When two pairs of electrons are shared it is called a double bond
When three pairs of electrons are shared it is called a triple bond

49. Polar and Nonpolar Molecules
While atoms share electrons to become stable they do not always share electrons equally
Some atoms have a stronger attraction to electrons than others
This unequal sharing makes one side of the bond more negative than the other
Polar bond: bond where the electrons are shared unevenly
Ex. Water molecules
Nonpolar bonds: bond where electrons are shared evenly

50. The Polar Water Molecule
2 hydrogen atoms and 1 oxygen atom bond together in a covalent bond
The oxygen has a greater share of the electrons (sharing one electron with each hydrogen)
The oxygen end has a negative charge
The hydrogen has a positive charge

51. Chemical Shorthand
In medieval times alchemists were the first to explore the world of chemistry
They believed in magic and mythical transformations
Discovered many properties of the elements
Created many symbols to represent the elements
Many are still used today
Alchemists, like me, were mainly concerned with transforming ordinary metals into gold

52. Symbols for Atoms Modern chemists use symbols to represent atoms
These symbols can be understood by chemists all over the world
Each element is represented by a one or two letter symbol
Many symbols are created by using the common name of the element
Ex. H for Hydrogen
Some symbols are creating by using the name of the element in another language
Ex. K for Potassium (which is called Kalium in Latin)

53. Symbols for Compounds
Compounds can be described using element symbols and numbers
Ex. H2
This tells us that there are 2 Hydrogen atoms in this molecule

54. Chemical Formulas
Chemical Formula: combination of chemical symbols and numbers which shows which elements are present in a compound
Ex. Ammonia or NH3
This tells you that the ratio is one nitrogen atom to three hydrogen atoms