This document provides information about the classification and structure of atoms and matter. It discusses the definitions of elements, compounds, and mixtures. It describes the atomic theory of John Dalton, including the law of conservation of mass and the law of constant composition. It explains the structure of atoms, including subatomic particles like protons, neutrons, and electrons. It discusses atomic mass, isotopes, and electron configuration. The periodic table is introduced, along with trends in atomic properties like size and ionization energy.

1. CHAPTER TWO
Atoms

2. Classification of Matter

3. 1)1) ElementElement isis a substance that consists of identical
atoms
•there are 116 known elements
•of these, 88 occur in nature
•their symbols consist of one or two
letters
Element Symbol
Carbon C
Calcium Ca
Oxygen O
Titanium Ti
•Symbols and element names are derived from a
variety of sources
Pure Substances

5. Relative Abundance of
Elements in Earth

6. 2)2) CompoundCompound is a pure substance made up of two
or more elements in a fixed ratio by mass
• The formula of a compoundThe formula of a compound tells us the ratios
of its constituent elements and identifies each
element by its atomic symbol.
NaCl: the ratio of sodium atoms to chlorine
atoms in sodium chloride is 1:1
H2O: the ratio of hydrogen atoms to
oxygen atoms in water is 2:1

7. Formula of Water

8. • are a combination of two or more pure
substances
•the substances may be present in any mass ratio
•each substance has a different set of physical
properties
•if we know the physical properties of the
individual components of the mixture, we can use
appropriate physical means to separate the
mixture into its component parts
Mixtures

10. Homogenous - uniform composition throughout
-gases, solutions, alloys
Heterogeneous - nonuniform composition throughout
-salad, trail mix, granite, chicken noodle soup

11. The symbol CO represents which of the following?
1. element
2. compound
3. homogeneous
mixture
4. heterogeneous
mixture

12. Monatomic elements:Monatomic elements: consist of single atoms; for
example, helium (He) and neon (Ne).
Diatomic elements:Diatomic elements: there are seven elements that
occur as diatomic molecules:
H2, N2, O2, F2, Cl2, Br2, and I2
Polyatomic elements:Polyatomic elements: some elements have three
or more atoms per molecule

13. 1. monoatomic element
2. diatomic element
3. polyatomic element
4. compound
S8 is an example of a ________.

14. All matter is composed of tiny ATOMSATOMS.
Atoms in an element have the same chemical properties.
Atoms of different elements have different properties.
COMPOUNDSCOMPOUNDS are formed by the chemical combination of
two or more different kinds of atoms.
A MOLECULEMOLECULE is a tightly bound combination of two or more
atoms that acts as a single unit.
Dalton’s Atomic Theory

15. 1) Law of Conservation of Mass1) Law of Conservation of Mass : matter can be
neither created or destroyed.
A chemical reaction just changes the attachments
among atoms, but does not destroy the atoms
themselves.
Evidence for Dalton’s Atomic Theory:

16. 2) Law of Constant Composition2) Law of Constant Composition: any
compound is always made up of elements in
the same proportion by mass
Ex. The mass ration of oxygen to hydrogen in pure water is
always 8:1
Evidence for Dalton’s Atomic Theory:
H2O

17. The unit of mass is the atomic mass unit (amu)atomic mass unit (amu)
1 amu = 1/12 the mass of a carbon atom
1 amu = 1.6605 x 10-24
g
What are atoms made of?
Subatomic Particles

18. +
+
+ +
+
+
+
+
-
-
-
-
-
-
-
-
• Protons and neutrons are found in the nucleus, and
electrons are found as a cloud outside the nucleus

19. I’m Professor
Thomson and I
discovered the
electrons in 1897
I used to be his graduate student.
Now I’m famous myself . I, Ernest
Rutherford discovered positive
charges in the nucleus in 1911

20. Cathode ray experiment (Thomson’s)
https://www.youtube.com/watch?v=_nLESblUAHY
Gold foil experiment (Rutherford’s)
https://www.youtube.com/watch?v=5pZj0u_XMbc

21. Mass number:Mass number: number of protons plus neutrons
Atomic number:Atomic number: number of protons
A carbon atom of this composition is referred to as
carbon-12.
Mass and Atomic Number

22. What is the mass number for an atom that
contains 7 electrons, 7 protons, and 8 neutrons?
1. 0
2. 7
3. 8
4. 15

23. What is the atomic number for an atom that
contains 7 electrons, 7 protons, and 8 neutrons?
1. 0
2. 7
3. 8
4. 15

24. Isotopes:Isotopes: atoms with the same number of
protons but a different number of neutrons.
carbon-12 has 6 protons and 6 neutrons
carbon-13 has 6 protons and 7 neutrons
carbon-14 has 6 protons and 8 neutrons
C13
6
C12
6
C14
6
Isotopes

25. Atomic weight:Atomic weight: the weighted average of the
masses (in amu) of the naturally occurring
isotopes of an element.
-Chlorine is 75.77% chlorine-35 and 24.23% chlorine-37
Atomic Weight

27. Periodic Table
Dimitri Mendeleev (1834-1907)
– arranged the known elements in order of increasing
atomic weight (rearranged by atomic number in 1913).
– He observed that when elements are arranged in this
manner, certain sets of properties recur periodically.
– He then arranged elements with recurring sets of
properties in the same columncolumn (vertical row).

28. Classification of elements

29. • MetalsMetals
– solids at room temperature (except mercury), shiny,
conduct electricity, and are ductile and malleable.
– form alloys (solutions of one metal dissolved in another);
brass, for example, is an alloy of copper and zinc.
– In chemical reactions, they tend to give up electrons.
• NonmetalsNonmetals
– Except for hydrogen (H), they lie on the right side of the
Periodic Table.
– Except for graphite, do not conduct electricity.
– In chemical reactions, they tend to accept electrons.
Classification of Elements

30. • MetaloidsMetaloids
– Share some of the properties with metals and nonmentals;
for example, they are shiny like metals but do not conduct
electricity
– Boron, silicon, germanium, arsenic, antimony, and tellurium
are classified as metalloids
– One of the metalloids, silicon, is a semiconductor; it does
not conduct electricity under certain applied voltages, but
becomes a conductor at higher applied voltages

32. Oxygen is an example of a(n) ________ element.
1. Main-group
2. Halogen
3. Transition metal
4. Noble gas

33. • The noble gases, Group 8A elements
Examples of Periodicity:

36. Shell
4
3
2
1
32
18
8
2
Relative
energies
of electrons
in each shell
lower
higher.
nucleus
1st shell
2nd shell
3rd shell
4th shell Number of
electrons shell
can hold
How are electron in an atom arranged?
Bohr’s Model

37. Electron configuration:Electron configuration: the exact arrangement
of electrons in the extranuclear space
The energy of electrons in an atom is
quantizedquantized, which means that an electron in
an atom can have only certain allowed
energies.
Ground-State electron configuration:Ground-State electron configuration: the
electron configuration of the lowest energy
state of an atom

38. Shell  Subshell  Orbital
Electron configuration continued…..Electron configuration continued…..
Within shells electrons are further groupedWithin shells electrons are further grouped
into 4 differentinto 4 different subshellssubshells, identified in, identified in
order of increasing energies:order of increasing energies: s, p, d, fs, p, d, f
Shell number: 1 2 3 4
Orbital designation: s s,p s,p,d s,p,d,f
Within each subshell electrons are groupedWithin each subshell electrons are grouped
intointo orbitalsorbitals, regions of space within an, regions of space within an
atom where the specific electrons are mostatom where the specific electrons are most
likely foundlikely found

39. ORBITALS HOLDS
S 1 orbital
P 3 orbitals
D 5 orbitals
F 7 orbitals
• each orbital hold only 2 electrons that differ in spin

42. • OOrbitals fill in the order of increasing energy
from lowest to highest.
• EEach orbital can hold up to two electrons
with spins paired Pauli’s principle.
• WWhen there is a set of orbitals of equal
energy, each orbital becomes half filled
before any of them becomes completely
filled Hund’s principle.

45. Orbital box diagramsOrbital box diagrams
Order: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p and so on……

46. Order: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p and so on……

47. Order: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p and so on……

48. Noble gas notationNoble gas notation
The symbol of the noble gas immediately preceding the particular
atom indicates the electron configuration of all filled shells
Electron
Configuration
(condensed)O rbital box diagram
Noble G as
Notation
1s
2
2s
2
2p
2
[He]2s
2
2p
2

51. Valence shell:Valence shell: the outermost incomplete shell.
Valence electron:Valence electron: an electron in the valence shell.
Lewis structure:Lewis structure: the symbol of the element represents
the nucleus and filled shells. Dots represent valence
electrons.

53. The Lewis Dot Structure for sulfur will contain _____ dots.
1. 4
2. 6
3. 8
4. 16

54. Periodicity of chemical properties can be
explained in terms of periodicity in electron
configuration.
The Periodic Table works because elements
in the same column (group) have the same
configuration in their outer shells.

55. The size of an atom is determined by the
size of its outermost occupied orbital.
The size of a chlorine atom is determined by the size of its three 3p orbitals, the
size of a carbon atom is determined by the size of if its three 2p orbitals.
198 pm
Cl Cl C C
1.54 pm
The radius of a chlorine
atom is 99 pm
The radius of a carbon
atom is 77 pm

56. Atomic Size
(picometers)
Explanation for this trend can be
found on page 56

57. • Ionization energy:Ionization energy: the energy required to
remove the most loosely held electron
from an atom in the gaseous state.
When lithium loses one electron, it becomes a lithium ion; it still
has three protons in its nucleus, but now only two electrons outside
the nucleus.

58. Increases across a row; valence electrons are in the same shell
and subject to increasing attraction as the number of protons in
the nucleus increases.
Increases going up a column; the valence electrons are in lower
energy levels, which are closer to the nucleus and feel the
nuclear charge more strongly.