Atoms

1
Chapter 17

• Atoms The Periodic Table

2
Elements

• Any material that is made up of only one type of
  atom is classified as an element
• Elements can exist as a solid, liquid or gas
• An element is a substance that cannot be broken
  down into simpler substances
• Atoms are the smallest particle that has the
  properties of an element
• Elements are not the smallest particle
• Elements have a set of properties

3
The Periodic Table

• Common elements are Carbon, Hydrogen, Nitrogen,
  Oxygen, Phosphorous, and Sulfur
• Oxygen is the most common in the human body and
  Iron is the most abundant on Earth
• Elements are arranged on the periodic table
  according to their chemical properties
• Properties of elements tend to change in a
  regular pattern when elements are arranged in
  order of increasing atomic number, or number of
  protons in their atoms

4
The History or the Periodic Table

• Mendeleev (1869) arranged the first table by
  atomic mass and found patterns
• His table had a few errors and was later
  rearranged by atomic number or number of protons
• The modern periodic table lead to the prediction
  and discovery of new elements.
• Hydrogen has one proton so it is atomic number
  one
• Helium has two protons so it is atomic number two
  and so on

5
Atomic Symbol

• The symbol comes from the letters of the
  elements name
• Carbon is C and Chlorine is Cl
• The first letter is always capitalized
• Note that CO is Carbon and Oxygen where Co is
  Cobalt
• Golds symbol is Au is from its Latin name Aurum
  and Lead is Pb after Plumbum

6
Hydrogen

• 90 of our Universe is made of Hydrogen
• Scientists propose that most of the elements on
  the periodic table were manufactured by the
  fusion of hydrogen atoms in stars that exploded
  long before our solar system developed
• Robert Brown (1827) noticed the movement of atoms
  while watching pollen grains under a microscope
• This is now known as Brownian motion
• His discovery was the first piece of evidence
  supporting the existence of atoms

7
The Atomic Nucleus Its Components

• The nucleus is the center of an atom made up of
  protons and neutrons called nucleons
• Protons are positively charged subatomic
  particles in the nucleus of the atom
• Neutrons are a neutral subatomic particle in the
  nucleus of an atom
• Electrons are tiny negatively charged subatomic
  particles moving around the outside of the
  nucleus of an atom
• Neutral atoms have equal numbers of protons
  electronsthe and neutralize each other

8
Nothing But Airor RatherSpace

• Electrons in the outer orbits repel one another
• This is called electrical repulsion
• The electrons will push away from each other
  creating mostly empty space within each atom
• Positive protons also have electrical repulsion
• Why are they able to exist in the nucleus
  together?

9
Atomic Numbers vs Mass Numbers

• Atomic numbers are the number of protons in the
  nucleus of the atom.
• Mass numbers are the total number of protons and
  neutrons in the nucleus of an atom
• If you know the atomic number, then you should
  know the number of protons
• This should tell you what element it is, its
  symbol, and how many electrons it has

• If your atomic number is 17 then you have 17
  protons, are Chlorine, and have 17 electrons
• If your mass number is 35 and your atomic number
  is 17, then you know that 17 n 35 so you have
  18 neutrons
• Uranium has a a mass of 238 and its atomic number
  is 92How many neutrons?

10
Concept Check

• How many protons are there in an iron atom? Its
  symbol is Fe and the atomic number is 26
• 26 protons
• How many electrons in a neutral Fe?
• 26 electrons
• How many neutrons?
• Remember the mass is the p n
• 56-26 30 neutrons

11
Isotopes

• Isotopes are any atom having the same number of
  protons but different numbers of neutrons
• You can never change the number of protons
  without changing the element
• You can change the number of electrons to make an
  ion
• You can change the number of neutrons to form an
  isotope

• If you change the number of neutrons then the
  mass number has to change
• Hydrogen has three isotopes Protium has 1,
  Deuterium has 2 and Tritium has 3 as a mass
• They are all a kind of hydrogen but have
  different mass numbers

12
Atomic Mass amu

• Average atomic mass is the weighted average of
  the masses of all naturally occurring isotopes of
  an element
• Atomic mass units or amus are a quantity equal
  to one-twelfth the mass of a carbon-12
  atomBasically the same as one proton
• Hydrogen had 3 isotopes with 3 different mass
  numbers but we can only list one on the periodic
  table

13
More Atomic Mass

• We average the three isotopes together to get an
  average called the atomic mass
• 1 2 3 6 ? 3 2 amu is not correct though
• We have to consider how much of each isotope is
  found in nature. By looking at the periodic table
  you will see that hydrogen is listed around 1 so
  therefore 1 is probably the most common isotope

14
Concept Check

• What is the difference between mass number and
  atomic mass?
• Mass number is the sum of the p, n, and e in one
  atom of an element
• Atomic mass (short for average atomic mass) is
  the average of the mass numbers
• The mass number is simply a counting number and
  doesnt need a unit where atomic mass needs to be
  measured in amus

15
Patterns Start To Emerge

• Once the elements were arranged into the periodic
  table by number of protons, patterns started to
  emerge
• The metals, nonmetals and metalloids were three
  groups that immediately lined up by properties
• The majority of the elements are the metals

16
The Metals

• The metals are the elements that are good
  conductors of heat and electricity
• They are ductile and malleable
• Alkali metals are soft and shiny and react
  violently with water. They are so reactive they
  are almost never found as an element. Ex Li
• Metals can be stretched in shape malleable
• Alkaline-Earth metals like Ca are less reactive
  and are commonly found in seashells, airplanes
  and even medicine

17
More Metals

• Transition metals are found in groups 3-12. They
  do form positive cation but are not as reactive.
  Most of our common uses are building structures,
  jewelry, surgical implants and bikes.
• Other cool metals are Cu used in wiring, tungsten
  used in light bulbs, Fe-Co-C-Mn used in our
  bodies, and Hg used in thermometers

18
The Nonmetals

• Nonmetals are the elements that are usually poor
  conductor of heat and electricity
• Nonmetals (except hydrogen) are found on the
  right hand side
• They can be s, l or g.
• Most are dull, and brittle
• Carbon is probably the most noted in sugar,
  graphite, diamonds, bucky balls, gasoline etc
• Nonmetals are plentiful on earth like O, N, and S

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Nonmetals Continued

• Group 16 is called the Chalcogens mainly due to
  Sulfer and Oxygen which are found in many ores
• Chalcogen is great for ore-forming
• The Halogens are a nonmetal family found in group
  17. They are highly reactive elements. Chlorine
  gas is an example that is used in pools
• Noble gases found in group 18 are also nonmetals.
  They do not react (inert) because they have 8
  electrons in their outermost orbit. Helium is
  used in balloons and argon is used in light bulbs.

20
Metalloids (Semiconductors)

• Semiconductors are the elements that are
  intermediate conductors of heat and electricity
• Semiconductors look like a nonmetal but can
  conduct electricity and heat under special
  circumstances
• Semiconductors are sometimes called metalloids

• There are only 6 semiconductors Boron, silicon,
  germanium, arsenic, antimony and tellurium
• Silicon makes up 28 of the mass of the Earths
  crust. It is the basic building block of sand,
  microchips, and other kinds of technology because
  of its use as a conductor. Charges also tend to
  stay on germanium and silicon in a grid like
  pattern

21
Synthetic Elements

• Synthetic elements do not occur naturally in
  nature and have to be created
• Technetium and Promethium are man made
• They are both radioactive
• Elements that are radioactive decay or break down
  into different elements
• Promethium is found in glow in the dark paint
• All elements over 92 are man made
• Americium is found in smoke detectors

22
Concept Check

• The elements copper (Cu), silver (Ag) and gold
  (Au) are three of the few metals that can be
  found naturally in their elemental states. These
  three metals have found great use as currency and
  jewelry for a number of reasons, including their
  resistance to corrosion and their remarkable
  colors. How is the fact that these metals have
  similar properties indicated in the periodic
  table?
• They are all in group 11 and should have similar
  physical and chemical properties

23
Periods and Groups

• Periods are the horizontal row of elements in the
  periodic table
• Groups or families are a vertical column of
  elements in the periodic table

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The Facts about Periods Groups

• Groups 1 and 2 have s level valence electrons
• Groups 3-12 have d level valence electrons
• Groups 13-18 have p level valence electrons
• The periods at the bottom are f level

• All the elements in a group have the same number
  of valence electrons
• Since they have the same number of valence
  electrons they all react about the same (chemical
  properties)

25
Periodic Trends

• As you follow across the periodic table you will
  notice the size of the atom decreases
• As you look down the groups of the periodic table
  you will notice the atoms size increases
• The patterns you may notice are sometimes called
  periodic trends or in other books periodic laws

26
Concept Check

• Which are larger atoms of cesium (Cs 55) or
  atoms of radon (Rn 86)?
• Cesium is further to the right of Radon in the
  same period
• Cesium would be larger in diameter

27
Skip It?

• If you scan period 6 you will notice some atomic
  numbers are missing
• These are located at the bottom of the periodic
  table and are called the inner transition metals
• The Lanthanides (follow element lanthanum) have
  similar chemical and physical properties
• The are difficult to purify but have practical
  uses such as LED bulbs
• The Actinides (follow element actinium) are also
  difficult to purify
• They are used in the nuclear power industry and
  actinides heavier than Uranium are man made