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Atoms and the

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How many protons, electrons and neutrons are in O2-? 10 p, 8 e, 8 n 8 p, 8 e, 8 n 8 p, 10 e, 8 n 8 p, 6 e, 8 n Every atom or ion of oxygen has 8 protons. – PowerPoint PPT presentation

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Title: Atoms and the


1
Atoms and the Periodic Table
2
Atomic Structure
  • ATOM the smallest particle that has the
    properties of an element.
  • From the early Greek concept of the atom to the
    modern atomic theory, scientists have built on
    and modified existing models of the atom.

3
ATOM BASICS
  • Atoms are composed of a positively charged
    nucleus surrounded by an electron cloud.
  • Nucleus (99 of atoms mass) uncharged neutrons
    and positively charged protons.
  • Electron cloud negatively charged electrons in
    constant motion creating a cloud like a fan.

4
DEMOCRITUS
  • In 400 B.C., this Greek philosopher suggested
    that the universe was made of indivisible units.
  • Atom (atomos) Greek word meaning unable to be
    divided

5
JOHN DALTON
In 1808, this English schoolteacher proposed his
own atomic theory that became widely accepted.
  • Daltons Atomic Theory
  • All elements are made of tiny atoms.
  • Atoms cannot be subdivided.
  • Atoms of the same element are exactly alike.
  • Atoms of different elements can join to form
    molecules.

Do these ideas still hold true today?
6
  • As it turns out, the atom can be divided into
    subatomic particles.
  • Thompson and Millikan are given credit for the
    first discoveries relating to electrons.

Millikan
Thompson
http//www.shs.d211.org/science/faculty/hlg/histor
y20of20atom20sanjay20karan/millikanpage.htm
7
Ernest Rutherford
  • Rutherford discovered the positively charged
    nucleus
  • (GOLD FOIL EXPERIMENT)

8
NIELS BOHR
  • In 1913, this Danish scientist suggested that
    electrons orbit the nucleus.
  • In Bohrs model, electrons are placed in
    different energy levels based on their distance
    from the nucleus.

9
Dmitri Mendeleev 1834-1907
1869 created first periodic table of
elements. Arranged elements in order of
increasing atomic mass.
10
Henry Moseley 1887-1915
One of Rutherfords students. 1914 Arranged the
elements in order of increasing atomic number
(responsible for TODAYS periodic table).
11
Electrons are like books in a book case. They can
only exist on certain levels.
12
Only certain orbits are allowed
13
The Bohr Atom was a Solar System model.
14
MODERN ATOMIC MODEL
  • By 1925, Bohrs model of the atom no longer
    explained all observations. Bohr was correct
    about energy levels, but wrong about electron
    movement.
  • Electrons occupy the lowest energy levels
    available.
  • Energy increases as distance from the nucleus
    increases.
  • Electrons move in patterns of wave functions
    around the nucleus.
  • It is impossible to know an electrons velocity
    and location at any moment in time (Schrödinger).

15
Schrödinger
This is very difficult stuff!
In 1926 Schrodinger proposes an equation that
gives the probability of finding an electron at
any place in the atom.
Dont worry, this wont be on the test.
16
ORBITALS
  • ORBITAL the regions in an atom where there is a
    high probability of finding electrons.
  • s is the lowest energy orbital, and p is slightly
    higher

s orbital
p orbitals
Dumbbell shaped
Spherical
17
  • d and f are the next two orbitals. They occupy
    even higher energy levels and take on more
    complex shapes than s p

18
VALENCE ELECTRONS
Carbon
4 valence electrons
  • Electrons in the outermost energy level are
    called VALENCE ELECTRONS.
  • Valence electrons determine how an atom will act
    in a chemical reaction.
  • Atoms with equal numbers of valence electrons
    have similar properties.
  • We will learn how to determine the of valence
    electrons in an atom later in this unit.

19
Organization of the Periodic Table
  • PERIODICITY regular variations (or patterns) of
    properties with increasing atomic number. Both
    chemical and physical properties vary in a
    periodic (repeating) pattern.

20
  • PERIOD horizontal row of elements on P.T.

21
  • GROUP (FAMILY)
  • vertical column of elements on P.T.

22
Periodic Key
of electrons of protons (in a neutral
atom) of neutrons A-Z
of protons Z
6 C Carbon 12.011
Atomic number (Z) Elements symbol Elements
name Atomic mass (A)
23
Determining P, N, and E- from chemical
symbols
Mass
  • Example 1 atom
  • protons 6
  • electrons 6
  • neutrons 14-6 8
  •  
  • Example 2 ion
  • protons 7
  • electrons 10
  • neutrons 15-7 8

No net charge
14 C 6
Atomic
15 N3- 7
Net charge of -3
24
ISOTOPES
  • Isotopes are atoms that have the same of
    protons, but a different of neutrons.
  • Example
  • Carbon-12 vs. Carbon-14
  • 12C
  • Mass 12 Atomic 6 (6P, 6E, 6N)
  • 14C
  • Mass 14 Atomic 6 (6P, 6E, 8N)

25
IONS
  • Ionization the process of adding or removing
    electrons from an atom or group of atoms.
  • An ion has a net electric charge.
  • Cation ion with a positive charge.
  • Ex Na
  • Anion ion with a negative charge.
  • Ex O2-

26
Valence electrons electron dot diagrams
  • Review The valence electrons are the outermost
    electrons in an atom. These are the electrons
    that are involved when there is a chemical
    reaction.
  • Looking at a periodic table, you can quickly
    determine how many valence electrons an atom has
    by what column it is in.

27
of Valence electrons
2
1
2
5
6
3
4
7
8
28
ELECTRON DOT DIAGRAMSvisual representations of
elements and their valence electrons
Standard form
6
3
R
1
4
2
7
8
5
Order of electron/dot placement
element symbol
Example
O
6 valence electrons
Oxygen
29
How many dots are in an electron dot diagram of
chlorine?
  1. 1
  2. 7
  3. 17
  4. 35

Cl
Chlorine and all of the other halogens (column
17) have seven valence electrons.
30
Review Questions
31
How many protons, electrons and neutrons are in
one atom of oxygen-17?
  1. 17 p, 17 e, 17 n
  2. 17 p, 17 e, 1 n
  3. 8 p, 8 e, 8 n
  4. 8 p, 8 e, 9 n

While most oxygen atoms have a mass of 16 g/mol,
oxygen-17 is an isotope with a mass of 17 g/mol.
The number of protons in an element is the same
for every atom of that element. electrons
protons if element has no charge.
32
The periodic law states that when elements are
arranged in order of increasing __________
_________, similarities in their properties occur
in a regular pattern.
  1. Atomic mass
  2. Atomic number
  3. Atomic radius

Moseley created the modern periodic table when he
determined that elements should be placed in
order of increasing atomic number ( of protons).
Its a shame that WWI took the life of this
brilliant scientist when he was so young.
33
Carbon-12 and carbon-14 are
  1. isomers
  2. isotopes
  3. radioactive elements
  4. different elements

Isotopes are atoms of the same element with
different numbers of neutrons, and therefore
different atomic masses. While carbon-14 is
used in radioactive dating, carbon-12 has a more
stable nucleus and therefore is not used in this
capacity.
34
How many protons, electrons and neutrons are in
O2-?
  1. 10 p, 8 e, 8 n
  2. 8 p, 8 e, 8 n
  3. 8 p, 10 e, 8 n
  4. 8 p, 6 e, 8 n

Every atom or ion of oxygen has 8 protons. The
net charge of -2 indicates that the ion has two
more negative charges (electrons) than positive
charges (protons) All atoms and ions of standard
oxygen-16 have 8 neutrons.
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