1. Elements, Atoms & Ions Chapter 41

2. Elements Over 112 known, of which 88 are found in nature
others are man-made
Abundance is the percentage found in nature
oxygen most abundant element (by mass) on earth and in the human body
the abundance and form of an element varies in different parts of the environment
Each element has a unique symbol
The symbol of an element may be one letter or two
if two letters, the second is lower case 2

3. Table 4.1: Distribution (Mass Percent) of the 18 Most Abundant Elements in the Earth's Crust, Oceans, and Atmosphere

4. Table 4.2: Abundance of elements in the human body

5. Dalton’s Atomic Theory
Elements are composed of atoms
tiny, hard, unbreakable, spheres
All atoms of a given element are identical
all carbon atoms have the same chemical and physical properties
Atoms of a given element are different from those of any other element
carbon atoms have different chemical and physical properties than sulfur atoms 3

6. Dalton’s Atomic Theory
Atoms of one element combine with atoms of other elements to form compounds.
Law of Constant Composition
all samples of a compound contain the same proportions (by mass) of the elements
Chemical Formulas 4

7. Dalton’s Atomic Theory
Atoms are indivisible in a chemical process.
all atoms present at beginning are present at the end
atoms are not created or destroyed, just rearranged
atoms of one element cannot change into atoms of another element
cannot turn Lead into Gold by a chemical reaction 5

8. Formulas Describe Compounds
a compound is a distinct substance that is composed of atoms of two or more elements
describe the compound by describing the number and type of each atom in the simplest unit of the compound
molecules or ions
each element represented by its letter symbol
the number of atoms of each element is written to the right of the element as a subscript
if there is only one atom, the 1 subscript is not written
polyatomic groups are placed in parentheses
if more than one 6

9. Figure 4.2: Dalton pictured compounds as collections of atmosphere NO, NO2, and N2O are represented

10. Are Atoms Really Unbreakable?
J.J. Thomson investigated a beam called a cathode ray
he determined that the ray was made of tiny negatively charged particles we call electrons
his measurements led him to conclude that these electrons were smaller than a hydrogen atom
if electrons are smaller than atoms, they must be pieces of atoms
if atoms have pieces, they must be breakable
Thomson also found that atoms of different elements all produced these same electrons 7

11. The Electron Tiny, negatively charged particle
Very light compared to mass of atom
1/1836th the mass of a H atom
Move very rapidly within the atom 8

12. Rutherford’s Results Over 98% of the  particles went straight through
About 2% of the  particles went through but were deflected by large angles
About 0.01% of the  particles bounced off the gold foil 11

13. Figure 4.6: (a) The results that the metal foil experiment would have yielded if the plum pudding model had been correct; (b) Actual results

14. Rutherford’s Nuclear Model
The atom contains a tiny dense center called the nucleus
the volume is about 1/10 trillionth the volume of the atom
The nucleus is essentially the entire mass of the atom
The nucleus is positively charged
the amount of positive charge of the nucleus balances the negative charge of the electrons
The electrons move around in the empty space of the atom surrounding the nucleus 12

15. Figure 4.9: A nuclear atom viewed in cross section

16. Structure of the Nucleus
The nucleus was found to be composed of two kinds of particles
Some of these particles are called protons
charge = +1
mass is about the same as a hydrogen atom
Since protons and electrons have the same amount of charge, for the atom to be neutral there must be equal numbers of protons and electrons
The other particle is called a neutron
has no charge
has a mass slightly more than a proton 13

17. The Modern Atom
We know atoms are composed of three main pieces - protons, neutrons and electrons
The nucleus contains protons and neutrons
The nucleus is only about cm in diameter
The electrons move outside the nucleus with an average distance of about 10-8 cm
therefore the radius of the atom is about 105 times larger than the radius of the nucleus 14

18. Isotopes All atoms of an element have the same number of protons
The number of protons in an atom of a given element is the same as the atomic number
found on the Periodic Table
Atoms of an element with different numbers of neutrons are called isotopes
All isotopes of an element are chemically identical
undergo the exact same chemical reactions
Isotopes of an element have different masses
Isotopes are identified by their mass numbers
mass number = protons + neutrons 15

19. Figure 4.10: Two isotopes of sodium

20. Elements Arranged in a pattern called the Periodic Table
Position on the table allows us to predict properties of the element
Metals
about 75% of all the elements
lustrous, malleable, ductile, conduct heat and electricity
Nonmetals
dull, brittle, insulators
Metalloids
also know as semi-metals
some properties of both metals & nonmetals 16

21. The Modern Periodic Table
Elements with similar chemical and physical properties are in the same column
Columns are called Groups or Families
Rows are called Periods
Each period shows the pattern of properties repeated in the next period 17

22. Figure 4.11: The periodic table

23. The Modern Periodic Table
Main Group = Representative Elements
“A” columns
Transition Elements
all metals
Bottom rows = Inner Transition Elements = Rare Earth Elements
metals
really belong in Period 6 & 7 18

24. Important Groups Noble Metals Ag, Au, Pt
Group 8 = Noble Gases
He, Ne, Ar, Kr, Xe, Rn
all colorless gases at room temperature
very non-reactive, practically inert
found in nature as a collection of separate atoms uncombined with other atoms
Noble Metals
Ag, Au, Pt
all solids at room temperature
least reactive metals
found in nature uncombined with other atoms 19

25. Important Groups - Halogens
Group 7A = Halogens
very reactive nonmetals
react with metals to form ionic compounds
HX all acids
Fluorine = F2
pale yellow gas
Chlorine = Cl2
pale green gas
Bromine = Br2
brown liquid that has lots of brown vapor over it
Only other liquid element at room conditions is the metal Hg
Iodine = I2
lustrous, purple solid 20

26. Allotropes
Many solid nonmetallic elements can exist in different forms with different physical properties, these are called allotropes
the different physical properties arise from the different arrangements of the atoms in the solid
Allotropes of Carbon include
diamond
graphite
buckminsterfullerene 21

27. Figure 4.18a: The three solid elemental (allotropes) forms of carbon

28. Figure 4.18b: The three solid elemental (allotropes) forms of carbon

29. Figure 4.18c: The three solid elemental (allotropes) forms of carbon

30. Electrical Nature of Matter
Most common pure substances are very poor conductors of electricity
with the exception of metals and graphite
Water is a very poor electrical conductor
Some substances dissolve in water to form a solution that conducts well - these are called electrolytes
When dissolved in water, electrolyte compounds break up into component ions
ions are atoms or groups of atoms that have an electrical charge 22

31. Figure 4.20: (a) Pure water does not conduct a current; (b) Water containing a dissolved salt conducts electricity

32. Ions ions that have a positive charge are called cations
form when an atom loses electrons
ions that have a negative charge are called anions
form when an atom gains electrons
ions with opposite charges attract
therefore cations and anions attract each other
moving ions conduct electricity
compound must have no total charge, therefore we must balance the numbers of cations and anions in a compound to get 0 total charge 23

33. Figure 4.21a: The arrangement of sodium ions (Na+) and chloride ions (Cl-) in the ionic compound sodium chloride.

34. Figure 4.21b: Solid sodium chloride highly magnified.

35. Atomic Structures of Ions
Metals form cations
For each positive charge the ion has 1 less electron than the neutral atom
Na = 11 e-, Na+ = 10 e-
Ca = 20 e-, Ca+2 = 18 e-
Cations are named the same as the metal
sodium Na  Na+ + 1e- sodium ion
calcium Ca  Ca+2 + 2e- calcium ion
The charge on a cation can be determined from the Group number on the Periodic Table for Groups IA, IIA, IIIA
Group 1A  +1, Group 2A  +2, (Al, Ga, In)  +3 24

36. Atomic Structures of Ions
Nonmetals form anions
For each negative charge the ion has 1 more electron than the neutral atom
F = 9 e-, F- = 10 e-
P = 15 e-, P3- = 18 e-
Anions are named by changing the ending of the name to -ide
fluorine F + 1e-  F- fluoride ion
oxygen O + 2e-  O2- oxide ion
The charge on an anion can be determined from the Group number on the Periodic Table
Group 7A  -1, Group 6A  -2 25