Chapter 2: The Components of Matter
2.5 The Atomic Theory Today
2.6 Elements: A First Look at the Periodic Table
2.7 Compounds: Introduction to Bonding
Clicker question #7
The definition of an element is:
a) A substance that consists of only one type of atom.
b) A substance that can be broken down into simpler substances
by physical or chemical means.
c) A substance that consists of multiple types of atoms.
d) A structure that consists of two or more atoms that are
chemically bound together
Clicker question #7
The definition of an element is:
a) A substance that consists of only one type of atom.
b) A substance that can be broken down into simpler substances
by physical or chemical means.
c) A substance that consists of multiple types of atoms.
d) A structure that consists of two or more atoms that are
chemically bound together
General features of the atom today.
•The atom is an electrically neutral, spherical entity composed of a positively
charged central nucleus surrounded by one or more negatively charged
electrons.
•The atomic nucleus consists of protons and neutrons.
Properties of the Three Key Subatomic Particles
Charge
Mass
Location
Name(Symbol) Relative Absolute(C)* Relative(amu)† Absolute(g) in the Atom
Proton (p+)
Neutron (n0)
Electron (e-)
1+ +1.60218x10-19
1.00727
0
0
1.00866
1-
-1.60218x10-19
0.00054858
1.67262x1024
1.67493x10-24 Nucleus
9.10939x10-28
* The coulomb (C) is the SI unit of charge.
†
Nucleus
The atomic mass unit (amu) equals 1.66054x10-24 g.
Outside
Nucleus
Atomic Symbols, Isotopes, Numbers
A
X
Z
The Symbol of the Atom or Isotope
X = Atomic symbol of the element
A = mass number; A = Z + N
Z = atomic number
(the number of protons in the nucleus)
N = number of neutrons in the nucleus
Isotope = atoms of an element with the same
number of protons, but a different number
of neutrons
Sample Problem 2.2
Determining the Number of Subatomic
Particles in the Isotopes of an Element
PROBLEM: How many protons, neutrons, and electrons are in the following
elements. What element symbols do Q and X represent?
a) 115 Q
b) 4120 X
Clicker question #8
Given 13153 Y. What element symbol does Y represent?
a) Na
b) I
c) Pt
d) Cs
Clicker question #8
Given 13153 Y. What element symbol does Y represent?
a) Na
b) I
c) Pt
d) Cs
Sample Problem 2.3
Calculating the Atomic Mass of an Element
Definition: amu or Da (atomic mass unit or Dalton) = 1/12 mass of 12C atom.
PROBLEM: Silver(Ag: Z = 47) has 46 known isotopes, but only two occur
naturally, 107Ag and 109Ag. Given the following mass
spectrometric data, calculate the atomic mass of Ag:
Isotope
107Ag
Mass(amu)
106.90509
Abundance(%)
51.84
109Ag
108.90476
48.16
The Modern Reassessment of the Atomic Theory
1. All matter is composed of atoms. The atom is the smallest body that
retains the unique identity of the element.
2. Atoms of one element cannot be converted into atoms of another
element in a chemical reaction. Elements can only be converted
into other elements in nuclear reactions.
3. All atoms of an element have the same number of protons and
electrons, which determines the chemical behavior of the element.
Isotopes of an element differ in the number of neutrons, and thus
in mass number. A sample of the element is treated as though its
atoms have an average mass.
4. Compounds are formed by the chemical combination of two or more
elements in specific ratios.
The modern periodic table.
Similar chemical properties
The modern periodic table.
Alkali metals
The modern periodic table.
Alkaline earth metals
The modern periodic table.
Halogens
The modern periodic table.
Noble gases
Clicker question #9
Using the periodic table, do you think Na and Cl have similar
chemical properties?
a) Yes, I think they have similar chemical properties.
b) No, I do not think they have similar chemical properties.
c) I can not tell from the periodic table whether they have similar
chemical properties.
d) This is a stupid question.
Clicker question #9
Using the periodic table, do you think Na and Cl have similar
chemical properties?
a) Yes, I think they have similar chemical properties.
b) No, I do not think they have similar chemical properties.
c) I can not tell from the periodic table whether they have similar
chemical properties.
d) This is a stupid question.
Bonding – ionic compounds
Formed from – the transfer of electrons from the atoms
of one element to those of another
Ions – charged particles
Cation – positively charged ion
Anion – negatively charged ion
Ionic compound formation animation
Sample Problem 2.4
Predicting the Ion and Element Forms
PROBLEM: What monatomic ions do the following elements form?
(a) Sulfur
(b) Rubidium
(c) Barium
Formation of a covalent bond between two H atoms.
Covalent bonds form when elements share electrons, which usually
occurs between nonmetals.
Elements that occur as molecules.
1A
2A
3A
4A
5A
6A
7A
8A
(1)
(2)
(13)
(14)
(15)
(16)
(17)
(18)
N2
O2
F2
P4
S8
Cl2
Se8
Br2
H2
I2
diatomic molecules
tetratomic molecules
octatomic molecules
Entities in covalent and ionic substances
Most covalent substances consist of molecules
No molecules exist in a sample of an ionic compound
Elements that are polyatomic.
A polyatomic ion