1. Unit 3 - Elements, Atoms and Ions
The Elements
Symbols for Elements
Dalton’s Atomic Theory
Formulas of Compounds
Structure of the Atom
Modern Concept of Atomic Structure
Isotopes
Introduction to the Periodic Table
Natural States of Elements
Ions
Compounds That Contain Ions
pages

2. Unit 3 - Elements, Atoms and Ions
Upon completion of this unit, you should be able to do the following:
Determine the number of protons, neutrons and electrons in an atom based on the element name or the atomic number and atomic mass.
Write the symbols of common elements and write the names of common elements given their symbols.
Differentiate between a chemical symbol and a chemical formula.
Explain the significance of subscripts .
Given a formula, state the number of atoms of each element present.
Use the periodic table to predict the charge and formula of a monatomic ion.
Use the periodic table to identify metals and non-metals.
Use the periodic table to identify alkali metals, alkaline earth metals, halogens and noble gases.

3. The Elements
Element – a substance that cannot be broken down into other substances by chemical methods.
Sometimes chemists use the word element is used to mean a single atom of that element. This is the microscopic form.
Other times the word element is used to mean a sample large enough to weigh on a balance. This is the macroscopic form.
The term element is also used in generic form. When we say the human body contains sodium, that does not mean elemental sodium is present, rather atoms of some form of sodium are present.

4. The Elements
Currently there are 118 elements, 88 of which occur naturally. The 9 most abundant elements listed below account for 98% of the mass of the earth’s crust.
Element
Mass Percent
Oxygen (O)
49.2
Silicon (Si)
25.7
Aluminum (Al)
7.50
Iron (Fe)
4.71
Calcium (Ca)
3.39
Sodium (Na)
2.63
Potassium (K)
2.40
Magnesium (Mg)
1.93
Hydrogen (H)
0.87

5. Symbols for Elements
Symbols are used as abbreviations for element names
One or two letters in symbol
First letter is upper case, second letter is lower case
Origin of some symbols come from Greek or Latin name
The symbol for lead is Pb from the Latin word for heavy, plumbum.
The name for bromine comes from a Greek word meaning stench.
Table 4.3 on page 87 lists 44 common elements with their symbols – memorize them

6. The Elements Song The Elements Song by
Tom Lehrer – Harvard scientist and musician
Background – song set to the tune of
“The Very Model of a Modern Major-General” from The Pirates of the Penzance
by Gilbert and Sullivan
Daniel Radcliffe version
Karaoke - Your Turn

7. Dalton’s Atomic Theory
Most natural materials are mixtures of pure substances.
Pure substances are either elements or combinations of elements called compounds.
A given compound always contains the same proportions (by mass) of the elements. This is known as the law of constant composition. For example, water always contains 8 grams of oxygen for each gram of hydrogen.

8. Dalton’s Atomic Theory
Elements are made of tiny particles called atoms.
All atoms of a given element are identical.
The atoms of a given element are different from those of any other element.
Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms.
Atoms are indivisible in chemical processes. Atoms are not created or destroyed in chemical reactions. The reaction only changes the way the atoms are grouped together.

9. Formulas of Compounds
Compound – a distinct substance that is composed of the atoms of two or more elements and always contains exactly the same relative masses of those elements. A compound can be broken down into those elements by chemical methods.
Example
Water (H2O) – can be broken down into hydrogen and oxygen. Water always contains 2 hydrogen atoms for each oxygen atom.

10. Formulas of Compounds
A chemical formula expresses the types of atoms and numbers of each atom in a given compound.
Water has 2 atoms of hydrogen for each atom of oxygen.
The chemical name for table salt is sodium chloride. The chemical formula for sodium chloride is NaCl. It contains 1 atom of sodium and 1 atom of chlorine.

11. Formulas of Compounds Rules for writing formulas
Each atom present is represented by its element symbol.
The number of each type of atom is indicated by a subscript written to the right of the element symbol.
When only 1 atom of a given type is present, the subscript 1 is not written.
Page 90, example 4.1
Self check exercise 4.1

12. Structure of the Atom
Scientists believed that elements consisted of atoms and that compounds are a specific collection of atoms bound together in some way.
But what is an atom like? Does it consist of smaller parts, and if so, what are the subatomic particles?
Video 1 - Atoms and the Periodic Table
Video 2 - J.J. Thomson and the electron
Video 3 - Ernest Rutherford and the nucleus

13. Structure of the Atom

14. Structure of the Atom Atoms consist of:
Electron – a negatively charged particle
Proton – a positively charged particle, same size of charge as an electron, but positive
Neutron – a neutral particle with a mass relatively close to that of proton
Protons and neutrons are located in a small dense center called the nucleus. Most of the mass of an atom is due to the nucleus.
Electrons are located outside of the nucleus in a negatively charged “cloud”. Most of the volume of an atom is due to the electrons.

15. Modern View of Atomic Structure
If all atoms are composed of the same components, why do different atoms have different chemical properties?
The answer lies in the number and arrangement of the electrons. The space in which the electrons move accounts for most of the atomic volume. The electrons are the parts of the atom that intermingle when atoms combine to form molecules. The number of electrons a given atom possesses greatly affects the way it can interact with other atoms.

16. Modern View of Atomic Structure
Electron cloud
1 Angstrom = 1 x meters

17. Isotopes
The identity of an element is determined by the number of protons it has. The number of protons is called the atomic number.
Isotopes of an element have the same number of protons, and therefore the same atomic number, but different numbers of neutrons.
The total number of protons and neutrons in an atom is called the mass number.
The mass number is used in naming to identify isotopes, such as Carbon-14, which has a mass number of 14. Carbon-12 has a mass number of 12.

18. Ag Isotopes 108 47 Silver A, mass number =
Z, atomic number =
Number of protons
108
A, mass number =
Number of protons and neutrons
X, element symbol

19. Isotopes Iodine - 127; 53 protons, 74 neutrons
Iodine-123 (half-life 13 hours) is the isotope of choice for nuclear medicine imaging of the thyroid gland, which naturally accumulates all iodine isotopes
HW - Page
Problems – 38 and 42

21. Metals Good conductors of heat and electricity Shiny (have luster)
Malleable - can be hammered into sheets
Ductile - can be drawn into wires

22. Nonmetals Good insulators (absorb electricity) Dull appearance
Most are gases or easily vaporized solids and liquids
Solids are brittle

23. Metalloids
Exhibits some properties of both metals and nonmetals.

24. Groups All elements in a group have similar chemical properties.
Group 1 Alkali Metals
Group 2 Alkaline Earth Metals
Groups 3-12 Transition Metals
Group 17 Halogens
Group 18 Noble Gases

25. Natural State of Elements
Gas
Liquid
Solid

26. Mnemonic to help remember - H2, I2, N2, Cl2, Br2, O2, F2 HINClBrOF
Diatomic Molecules
Mnemonic to help remember - H2, I2, N2, Cl2, Br2, O2, F2 HINClBrOF
Or 7 from 7 + H

27. Ions
An atom has a certain number of protons in its nucleus and an equal number of electrons in the space around the nucleus, giving the atom a net zero charge.
Adding or removing an electron from a neutral atom will create a charged ion.
Ions are always formed by adding or removing electrons, not by changing the number of protons.

28. Ions
A positive ion, called a cation, is produced when an atom loses one or more electrons.
Na → Na+ + e-
A cation is named using the name of the parent atom. Na+ is called the sodium ion.

29. Ions
A negative ion, called an anion, is produced when an atom gains one or more electrons.
Cl + e Cl-
An anion is named by taking the root name of the atom and changing the ending. Cl- is called the chloride ion.

30. Ions
Similarly, other Group 17 nonmetals gain one electron to form anions. The fluorine anion is called fluoride, the bromine anion is called bromide and the iodine anion is called iodide.
Oxygen and sulfur add two electrons to form anions. The oxygen anion is called oxide and the sulfur anion is called sulfide.

31. Ions
Atoms do not form ions on their own. Most commonly, ions are formed when metallic elements combine with nonmetallic elements.
When metals and nonmetals react, the metal atoms tend to lose one or more electrons, which are gained by the atoms of the nonmetals.
Reactions between metals and nonmetals tend to form compounds that contain metal cations and nonmetal anions.

32. Ions Group 1 metals form ions with a +1 charge
Many Group 3-12 metals form ions with multiple charges
Group 17 atoms form ions with a -1 charge
Group 16 atoms form ions with a -2 charge
Metals always form cations.
The tendency to lose electrons is a fundamental characteristic of metals.

33. Compounds that contain Ions
Sodium Chloride example
NaCl is a solid and does not conduct electricity
Pure (distilled) water does not conduct electricity
NaCl dissolved in water does conduct electricity
Why?

34. Compounds that contain Ions
Electric current can travel when electrons are free to move.
In ionic substances, ions carry the current
Substances that contain ions can conduct an electric current only if the ions can move.
Distilled water contains no ions.
When NaCl is dissolved in water it ionizes and the electrons are free to move.

35. Compounds that contain Ions
Whenever a compound is formed between a metal and non-metal, it can be expected to contain ions.
These substances are called ionic compounds. A chemical compound must have a net charge of zero.
There must be positive ions (cations) and negative ions (anions) present.
The number of cations and anions must result in a net charge of zero.
When writing the formula for a compound, the cation is always written first.
Use subscripts to balance charges on compounds.

36. Compounds that contain Ions
Writing Formulas
Examples: Na+ + Cl- → NaCl
Mg Cl- → MgCl2
Al 3+ + Cl- → AlCl3
Li + + N 3- → Li3N
Practice Ca 2+ + Cl- →
Na + + S2- →
Ca 2+ + P 3- →
Homework
Page 119 – problems 76, 78, 84