Atomic Structure

1
Atomic Structure

• Chapter 2
• Applied

2
What is an atom?

• An atom is the smallest particle of a given type
  of matter.
• If the hydrogen atom was the size of a soccer
  ball, then a soccer ball would be 6450 kilometers
  (4008 miles) high.

3
Atomic Structure

• An atom consists of three subatomic particles
  protons, neutrons and electrons
• Protons are positively charged particles located
  in the nucleus, or center, of the atom.
• Neutrons are neutral particles located in the
  nucleus. Neutrons and protons have approximately
  the same mass.
• Electrons are negatively charged particles that
  are located outside the nucleus in the electron
  cloud.

4
Atoms
5
Atoms

• Atoms are neutral particles, so they have equal
  numbers of protons and electrons.
• http//education.jlab.org/atomtour/listofparticles
  .html

6
Symbols of elements

• 9038Sr

The mass number is equal to the sum of the
protons and neutrons. The atomic number is
equal to the number of protons. So, to get the
number of neutrons, you subtract.
Mass number
Atomic number
7
Bohr Diagram

• How many protons are there?
• How many neutrons?
• How many electrons?
• What is the charge of this atom?
• What is the charge of the nucleus of this atom?
• This is an atom of what element?

8
Atoms Vs. Ions

• Atoms are neutral particles.
• Ions are charged particles formed when atoms gain
  or lose electrons.
• Since electrons are negative, when an atom gains
  electrons, it becomes a negative ion.
• When an atom loses electrons, it becomes positive.

9
Valence electrons and ions

• To determine what kind of ion an atom will form,
  look at the number of valence electrons, or the
  last number in the electron configuration. The
  valence electrons are on the outermost energy
  level.
• If there are less than 4, the atom will lose the
  electrons. If there are 5-7, the atom will gain
  the corresponding number required to make 8. If
  there are 4, the atom can do either.

10
Ions

• Look up potassium (K) on your periodic table.
• The electron configuration is 2-8-8-1, so it has
  1 valence electron.
• It will lose this electron, and form a 1 ion.
• The ion still has 19 positive protons, but only
  18 negative electrons, so 19
  (-18) 1

11
Ions

• Look up phosphorus (P) on your periodic table.
• Its electron configuration is 2-8-5, so it has 5
  valence electrons. It needs to gain 3 more to
  make 8. It will form a negative ion since it
  will be gaining electrons.
• The phosphorus ion will still have 15 protons,
  but it will have 18 negative electrons, so 15
  (-18) -3

12
Interactive site

• http//web.visionlearning.com/custom/chemistry/ani
  mations/CHE1.3-an-atoms.shtml

http//science.widener.edu/svb/tutorial/protons.ht
ml
13
Isotopes

• Atoms of the same element can have a different
  number of neutrons. These atoms are called
  isotopes.
• The atomic number, and therefore, number of
  protons stays the same since its the same
  element, but the mass number and number of
  neutrons changes.

14
Isotopes

• 146C and 126C are isotopes. Both have 6 protons
  and 6 electrons, but 146C has 8 neutrons and 126C
  has 6 neutrons.
• Cl-35 and Cl-37 are isotopes. Both have 17
  protons (see atomic number) and 17 electrons, but
  Cl-35 has 18 neutrons and Cl-37 has 20 neutrons.

15
Isotopes