Matter Is Made Up Of Atoms

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• Matter Is Made Up Of Atoms

Chapter 4
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I CAN describe the parts of an atom and the
particles that make them up.
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Structure of the Atom

• An atom is the smallest particle of matter that
  retains all of matters properties.
• Atoms have TWO PARTS
• A NUCLEUS
• An ELECTRON CLOUD

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A Model of the Atom
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The Nucleus of the Atom

• The NUCLEUS of the atom is the SMALL, DENSE,
  SOLID central region of the atom.
• The NUCLEUS is made up of TWO smaller particles
  sub-atomic particles called
• PROTONS and NEUTRONS

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PROTONS

• PROTONS are sub-atomic particles that have a
  POSITIVE ELECTRICAL CHARGE.
• Represented by the symbol P
• The most important thing about protons is that
  they identity of an element.

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The ATOMIC NUMBER (AN)

• The number of PROTONS in an atoms nucleus is
  called the ATOMIC NUMBER of the atom.
• Atoms can have from 1 to 109 protons, depending
  on which element is being referenced.
• The number of PROTONS determines which element an
  atom belongs to.

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NEUTRONS

• NEUTRONS are the other subatomic particle found
  in the atoms nucleus.
• NEUTRONS are NEUTRAL they have NO ELECTRICAL
  CHARGE.
• The symbol for a NEUTRON is No

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The ATOMIC MASS NUMBER (AMN)

• The ATOMIC MASS NUMBER is the COMBINED NUMBER of
  PROTONS and NEUTRONS in the atoms nucleus.
• Together, the protons and neutrons are
  responsible for 99.999 of the atoms total mass.

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PRACTICE PROBLEMS

• An atom has 12 protons and 14 neutrons.
• a. What is the atomic number of the
• atom? ____________
• b. The atomic mass number ?_______
• An atom contains 33 protons and 41 neutrons.
• AN ________ AMN ________

12 (12 P)
26 (12 P plus 14 No)
33 (33 P)
74 (33 P plus 41 No)
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• Look at a Periodic Table.
• The Atomic Mass Number is found at the BOTTOM of
  each elements square.
• Now look at the ATOMIC MASS NUMBERS for the
  elements.
• What do you notice about these numbers?
• THEY CONTAIN DECIMALS

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How do atomic mass numbers get their decimals?

• We learned earlier that the AMN is the total of
  an atoms protons and neutrons combined.
• How can this give a number with a decimal?

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• While ALL atoms of an element have the SAME
  NUMBER of PROTONS they dont all have the same
  number of NEUTRONS.
• The number of NEUTRONS can vary between atoms of
  the same element.

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ISOTOPES

• Atoms of an element that have differing numbers
  of NEUTRONS are called ISOTOPES.
• The ATOMIC MASS NUMBER reported for an element on
  the PERIODIC TABLE is an AVERAGE of all the
  different ISOTOPES of that element.

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Writing Isotopes

• Isotopes can be written two ways
• 1. Write the CHEMICAL SYMBOL and AMN
• Example C-14
• 2. Write the CHEMICAL SYMBOL with AN
• and AMN
• Example 14 C
• 6

AMN on top AN
on bottom
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The Electron Cloud

• Unlike the NUCLEUS, the ELECTRON CLOUD
• Is very large about 10,000x the size of the
  nucleus.
• Is NOT solid it is an area of EMPTY SPACE
  surrounding the nucleus.
• Contains only one subatomic particle.

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The ELECTRON

• The ELECTRON is the smallest of the sub-atomic
  particles.
• It takes 1834 electrons to have about the same
  mass as ONE proton!
• The symbol for an electron is e-
• Neutral atoms have as many electrons as they do
  protons!
• The ATOMIC NUMBER is also the number of
  electrons in the Electron Cloud.

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Divisions of the Electron Cloud

• The Electron Cloud is divided into 7 main regions
  called PRINCIPLE ENERGY LEVELS.
• The PELs move outward away from the nucleus1 is
  closest.7 is farthest away!
• Each PEL can hold a certain number of electrons.

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• PEL 1 2 e-
• PEL 2 8 e-
• PEL 3 18 e-
• PEL 4 32 e-
• PEL 5 32 e-
• PEL 6 32 e-
• PEL 7 32 e-

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Sublevels

• Each PEL can further be divided into smaller
  divisions called SUBLEVELS.
• The number of sublevels in a PEL depends on its
  distance from the nucleus.

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• PEL 1 has only 1 sublevel, called S
• PEL 2 has two sublevels S and P
• PEL 3 has three sublevels S, P and D
• PEL 4-7 has four sublevels S, P, D and F
• S sublevels are spherical and hold a max of 2 e-.
• P sublevels are figure 8-like and hold a max of
  6e-.

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• D sublevels are mushroom shaped and lie along
  the X, Y, Z plane.
• D sublevels hold a max of 10 e-.
• F sublevels assume different shapes along the X,
  Y, Z plane and hold a max of 14 e-.

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Sublevel Filling Patterns

• Because the energy required to maintain the orbit
  of the more complex sublevels is more than that
  of more simple orbits, a sublevel will not
  completely fill before the next higher one begins
  receiving electron.

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AUFBAU Electron Distribution Chart

• 1s
• 2s 2p(10)
  Ne 10
• 3s 3p(18)3d Ar18
• 4s 4p(36)4d 4f Kr36
• 5s 5p(54)5d 5f Xe54
• 6s 6p(86) 6d 6f Rn86
• 7s 7p 7d 7f

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Orbital Notation

• Orbital Notation is used to illustrated the
  distribution of e- within the e- cloud.
• Number of e-
  in sublevels
• Example Mg 1s2 2s2 2p6 3s2
• Symbol Sublevels

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Practice Problems

• Write out the electron configuration of
• 1. Oxygen
• 2. Calcium
• 3. Iodine

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Shorthand e- Configurations

• Locate the NOBLE GAS immediately before the
  element.
• Write the noble gas symbol in a bracket
• example Xe
• Subtract the AN of the noble gas from the
  element, then distribute the remaining electrons
  beginning at the next sublevel.

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Practice

• Write the shorthand configuration for Barium.
• Ba 56 e- nearest noble gas is Xe
• with 54 e-. Xe fills the
  sublevels through 5p.
• 56 54 2 e- to distribute beginning at 6s.

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• Ba Xe 6s2
• Practice
• Write shorthand configurations for
• A. Arsenic
• B. Iodine

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• The most important PEL is the outermost one of
  the atom.
• The electrons on this level are involved in
  forming chemical bonds with other atoms. The
  electrons in the outermost PEL are known as
• VALENCE ELECTRONS,
• or Ve- for short.