1. Chemical Foundations: Elements, Atoms, and Ions
Chapter 4
Chemical Foundations: Elements, Atoms, and Ions
Copyright © Cengage Learning. All rights reserved

2. 118 known: 88 found in nature, others are made in laboratories.
Abundance is the percentage found in nature.
Oxygen most abundant element (by mass) on earth and in the human body.
Copyright © Cengage Learning. All rights reserved

3. Each element has a unique one- or two-letter symbol.
First letter is always capitalized and the second is not.
The symbol usually consists of the first one or two letters of the element’s name.
Examples: Oxygen O Krypton Kr
Sometimes the symbol is taken from the element’s original Latin or Greek name.
Examples: Gold Au aurum Lead Pb plumbum
Copyright © Cengage Learning. All rights reserved

4. Dalton’s Atomic Theory (1808)
Elements are made of tiny particles called 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.
Copyright © Cengage Learning. All rights reserved

5. Law of Constant Composition
4. 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.
A given compound always has the same composition, regardless of where it comes from.
Water always contains 8 g of oxygen for every 1 g of hydrogen.
Carbon dioxide always contains 2.7 g of oxygen for every 1 g of carbon.
Copyright © Cengage Learning. All rights reserved

6. Dalton’s Atomic Theory (continued)
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.
Copyright © Cengage Learning. All rights reserved

7. Dalton’s Atomic Theory (continued)
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 (Lead cannot be turned into Gold by a chemical reaction)
Copyright © Cengage Learning. All rights reserved

8. Concept Check
Which of the following statements regarding Dalton’s atomic theory are still believed to be true?
Elements are made of tiny particles called atoms.
All atoms of a given element are identical.
A given compound always has the same relative
numbers and types of atoms.
IV. Atoms are indestructible.
Statements I and III are true. Statement II is not true (due to isotopes and ions). Statement IV is not true (due to nuclear chemistry).
Copyright © Cengage Learning. All rights reserved

9. Chemical Formulas Describe Compounds
Compound – distinct substance that is composed of the atoms of two or more elements and always contains exactly the same relative masses of those elements.
Chemical Formulas – expresses the types of atoms and the number of each type in each unit (molecule) of a given compound.
Copyright © Cengage Learning. All rights reserved

10. 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 one atom of a given type is present, the subscript 1 is not written.
Copyright © Cengage Learning. All rights reserved

11. Exercise
The pesticide known as DDT paralyzes insects by binding to their nerve cells, leading to uncontrolled firing of the nerves. Before most uses of DDT were banned in the U.S., many insects had developed a resistance to it. Write out the formula for DDT. It contains 14 carbon atoms, 9 hydrogen atoms, and 5 atoms of chlorine.
C14H9Cl5
C14H9Cl5
Copyright © Cengage Learning. All rights reserved

12. Investigated a beam called a cathode ray
J. J. Thomson (1898—1903)
Investigated a beam called a cathode ray
He determined that the ray was made of tiny negatively charge 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 the atom. The atom must be breakable.
He found that atoms of different elements all produce these electrons.
Copyright © Cengage Learning. All rights reserved

13. The ELECTRON - Tiny, negatively charge particle - Very light compared to the mass of the atom. ( 1/1836th the mass of a Hydrogen atom. - Move very rapidly within the atom
Copyright © Cengage Learning. All rights reserved

14. William Thomson (Plum Pudding Model)
Reasoned that the atom might be thought of as a uniform “pudding” of positive charge with enough negative electrons scattered within to counterbalance that positive charge.
Copyright © Cengage Learning. All rights reserved

15. Thomson’s Plum Pudding Model
The atom IS breakable!!
The atom has structure.
Electrons suspended in a positively charge electric field. – must have positive charge to balance negative charge of electrons and make the atom neutral.
Mass of the atom is due to electrons.
Atom is mostly “empty” space compared size of the electrons to size of the atom
Copyright © Cengage Learning. All rights reserved

16. Rutherford’s Gold Foil Experment
How can you prove something is empty?
put something through it
use large target atoms
use very thin sheets of target so do not absorb “bullet”
use very small particle as bullet with very high energy
but not so small that electrons will affect it
bullet = alpha particles, target atoms = gold foil
 particles have a mass of 4 amu & charge of +2 c.u.
gold has a mass of 197 amu & is very malleable
Copyright © Cengage Learning. All rights reserved

17. Rutherford’s experiment on α-particle bombardment of metal foil.
Copyright © Cengage Learning. All rights reserved

18. Over 98% of the  particles went straight through
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
Copyright © Cengage Learning. All rights reserved

19. (a) The results that the metal foil experiment would have yielded if the plum pudding model had been correct. (b) Actual results.
Copyright © Cengage Learning. All rights reserved

20. Explained the nuclear atom.
Ernest Rutherford (1911)
Explained the nuclear atom.
Atom has a dense center of positive charge called the nucleus.
Electrons travel around the nucleus in the empty space at a relatively large distance.
A proton has the same magnitude of charge as the electron, but its charge is positive.
Copyright © Cengage Learning. All rights reserved

21. Rutherford and Chadwick (1932)
Most nuclei also contain a neutral particle called the neutron.
A neutron is slightly more massive than a proton but has no charge.
Copyright © Cengage Learning. All rights reserved

22. 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
Copyright © Cengage Learning. All rights reserved

23. Electrons – found outside the nucleus; negatively charged
The atom contains:
Electrons – found outside the nucleus; negatively charged
Protons – found in the nucleus; positive charge equal in magnitude to the electron’s negative charge
Neutrons – found in the nucleus; no charge; virtually same mass as a proton
Copyright © Cengage Learning. All rights reserved

24. Small compared with the overall size of the atom.
The nucleus is:
Small compared with the overall size of the atom.
Extremely dense; accounts for almost all of the atom’s mass.
Copyright © Cengage Learning. All rights reserved

25. Copyright © Cengage Learning. All rights reserved

26. A nuclear atom viewed in cross section.
Copyright © Cengage Learning. All rights reserved

27. Why do different atoms have different chemical properties?
The chemistry of an atom arises from its electrons.
Electrons are the parts of atoms that “intermingle” when atoms combine to form molecules.
It is the number of electrons that really determines chemical behavior.
Copyright © Cengage Learning. All rights reserved

28. In nature most elements contain mixtures of isotopes.
Atoms with the same number of protons but different numbers of neutrons.
Show almost identical chemical properties; chemistry of atom is due to its electrons.
In nature most elements contain mixtures of isotopes.
Copyright © Cengage Learning. All rights reserved

29. Two Isotopes of Sodium
Copyright © Cengage Learning. All rights reserved

30. X = the symbol of the element
Isotopes
X = the symbol of the element
A = the mass number (# of protons and neutrons)
Z = the atomic number (# of protons)
Copyright © Cengage Learning. All rights reserved

31. Isotopes – An Example Name of element carbon Number of protons
Number of neutrons
(8 neutrons)
Name of element
carbon
Number of protons
(6 protons)
Number of neutrons
(6 neutrons)
Copyright © Cengage Learning. All rights reserved

32. What is the mass number of this isotope? Identify the element.
Exercise
A certain isotope X contains 23 protons and 28 neutrons.
What is the mass number of this isotope?
Identify the element.
Mass Number = 51 Vanadium
The mass number is 51. Mass Number = # protons + # neutrons. Mass Number = = 51. The element is vanadium. The number of protons determines the identity of the element.
Copyright © Cengage Learning. All rights reserved

33. Arranged in a pattern called the Periodic Table
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
Copyright © Cengage Learning. All rights reserved

34. The Periodic Table
The periodic table shows all of the known elements in order of increasing atomic number.
Copyright © Cengage Learning. All rights reserved

35. Periods – horizontal rows of elements
The Periodic Table
Metals vs. Nonmetals
Groups or Families – elements in the same vertical columns; have similar chemical properties
Periods – horizontal rows of elements
Copyright © Cengage Learning. All rights reserved

36. Most elements are metals and occur on the left side.
The Periodic Table
Most elements are metals and occur on the left side.
The nonmetals appear on the right side.
Metalloids are elements that have some metallic and some nonmetallic properties.
Copyright © Cengage Learning. All rights reserved

37. Physical Properties of Metals
Efficient conduction of heat and electricity
Malleability (they can be hammered into thin sheets)
Ductility (they can be pulled into wires)
A lustrous (shiny) appearance
Copyright © Cengage Learning. All rights reserved

38. Physical Properties of Nonmetals
Lack properties of metals
Exhibit much variation in properties
Can be gases, liquids, or solids
Copyright © Cengage Learning. All rights reserved

39. Physical Properties of Metalloids
Exhibit a mixture of metallic and non-metallic properties
Copyright © Cengage Learning. All rights reserved

40. Most elements are very reactive.
Elements are not generally found in uncombined form.
Exceptions are:
Noble metals – gold, platinum and silver
Noble gases – Group 8
Copyright © Cengage Learning. All rights reserved

41. Diatomic Molecules Nitrogen gas contains N2 molecules.
Oxygen gas contains O2 molecules.
Copyright © Cengage Learning. All rights reserved

42. Diatomic Molecules
Copyright © Cengage Learning. All rights reserved

43. Important Group - 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
Copyright © Cengage Learning. All rights reserved

44. Different forms of a given element. Example:
Allotropes
Many solid nonmetallic elements can exist in different forms with different physical properties, these are called allotopes.
Different forms of a given element.
Example:
Solid carbon occurs in three forms.
Diamond
Graphite
Buckminsterfullerene
Copyright © Cengage Learning. All rights reserved

45. Carbon Allotropes
Copyright © Cengage Learning. All rights reserved

46. Atoms can form ions by gaining or losing electrons.
Metals tend to lose one or more electrons to form positive ions called cations.
Cations are generally named by using the name of the parent atom.
Copyright © Cengage Learning. All rights reserved

47. Nonmetals tend to gain one or more electrons to form negative ions called anions.
Anions are named by using the root of the atom name followed by the suffix –ide.
Copyright © Cengage Learning. All rights reserved

48. Ion Charges and the Periodic Table
The ion that a particular atom will form can be predicted from the periodic table.
Group or Family
Charge
Alkali Metals (1A) 1+
Alkaline Earth Metals (2A) 2+
Halogens (7A) 1–
Noble Gases (8A)
Copyright © Cengage Learning. All rights reserved

49. Ion Charges and the Periodic Table
Copyright © Cengage Learning. All rights reserved

50. Electrical Nature of Matter
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
Copyright © Cengage Learning. All rights reserved

51. Exercise
An ion with a 3+ charge contains 23 electrons. Which ion is it? a) Fe3+ b) V3+ c) Ca3+ d) Sc3+
The 3+ charge on the ion means that the ion has lost 3 electrons, therefore the number of protons is 26 (23+3). The ion is Fe3+.
Copyright © Cengage Learning. All rights reserved

52. A certain ion X+ contains 54 electrons and 78 neutrons.
Exercise
A certain ion X+ contains 54 electrons and 78 neutrons.
What is the mass number of this ion?
133
The mass number is 133. The plus charge in X+ means that the ion has lost an electron, therefore the number of protons is 55 (54+1). The ion is Cs+ with a mass number of 133 (55+78).
Copyright © Cengage Learning. All rights reserved