Unit 5 – Atoms & the Periodic Table
Unit Big Idea: The atomic structure of an element determines the properties of the element and
determines how the element interacts with other elements.
Lesson 1 – Introduction to Energy
Essential Question: How do we know what parts make up the atom?
By the end of this lesson, you should be able to describe how the development of the atomic theory has
led to the modern understanding of the atom and its parts.
- Atom – smallest particle into which an element can be divided and still be the same element
- basic unit of matter
- smallest unit that has the chemical properties of an element
- make up everything that you see both natural and man made
- so tiny they can only been seen with an electron microscope
Creation of the ATOMIC THEORY & how it changed over time
- Dalton’s atomic theory – Billiard Ball Model
- 1808, John Dalton, a British chemist published the first theory about atoms that was based on
evidence gathered from experiments
- this theory explained most observations about matter but needed to be revised to explain
everything
- ALL MATTER IS MADE UP OF ATOMS – atoms can’t be created, divided, or destroyed; &
all atoms of a certain element are identical but different from atoms of other elements
- atoms join together to make new substances & every substance is made up of atoms combined
in specific ways
- Thompson’s change to the atomic theory – also known as the Plum Pudding Model
- In 1897 J.J. Thomson discovered atoms are made up of even smaller particles he called electrons
- electrons – negatively charged particles found within the atom
- an atom is a positive sphere with electrons mixed through it
- Rutherford’s change to the atomic theory - In 1909 Ernest Rutherford discovered the nucleus
- nucleus – small, dense center that has a positive charge and a is surrounded by moving electrons
- nucleus made of smaller particles that are positively charged – called them protons
- protons – positively charged particles found within the nucleus
- Bohr’s change to the atomic theory – also known as the Planetary Model
- atoms have a positive nucleus surrounded by electrons but the electrons move around the
nucleus in circular paths like planets orbiting the sun
- each path of the electron has a certain distance from the nucleus
- there are specific numbers of electrons that are in each orbit – if the entire field is filled up, the
element is considered stable and won’t bond with other elements – if the last orbit field is not
filled up the atom may give off electrons or share electrons with other atoms to fill up the outer
most field – this is called chemical bonding
- valance electrons are the electrons in the outermost circle of the atom
- helps predict the chemical properties of elements by looking at how many valance electrons are
in the outer most orbit
- atoms emit energy when an electron jumps to an orbit field closer to the nucleus & absorb
energy when an electron jumps to a field further out from the nucleus
- The 1st electron shell holds only 2 electrons, the 2nd electron shell holds only 8 electrons, and the
3rd electron shell holds only 18 elections.
- Modern Atomic Theory – based on work of many scientists over many years
- Keeps the following ideas:
- Dalton’s idea that atoms are the basic unit of matter and that atoms of each element are unique
- Thomson’s idea that atoms are made up of electrons.
- Rutherford’s idea that atoms are made up of protons.
- James Chadwick’s discovery of an uncharged particle, the neutron is in the nucleus.
- New ideas:
- Electrons don’t move in circular paths around the nucleus but move within an area around the
nucleus called the electron cloud, as seen in the picture to the right.
- The idea of the electron cloud says that we can’t know exactly where an electron is inside the
atom without changing its location when looking at it. There are certain places electrons are
more likely to be. You are more likely to find electrons in the darker shaded areas than in the
lighter shaded areas or the un-shaded areas.
- Parts of an atom:
- unified atomic mass unit (amu or u) is new unit created for the very small masses of atomic
particles
- protons are positively charged and found in the nucleus
- the charge of a proton is written 1+
- mass of proton is very small – 1.7 x 10-24
- protons have a mass of about 1 amu.
- the number of protons in an atom is the same as the
number of electrons in an atom
- neutrons have no electric charge
- neutrons slightly larger than a proton but still have
a mass of about 1 amu.
- atoms have at least as many neutrons as they have protons
- nucleus of an atoms has both protons and neutrons and is located in the center of the atom
- the nucleus has a positive charge, the amount of protons in the nucleus, since neutrons
don’t have a charge
- the protons and neutrons in the nucleus are have the most mass of the atom
- electrons have the negative charge in the atom & move around outside the nucleus very rapidly
- we can’t figure out their exact position and speed at the same time, by finding out one,
we change the other
- electrons have very little mass – about 0 amu.
- the charge of an electron is written 1- the charge of protons and electrons are opposite but equal – the number of electrons in an
atom is the exact same as the number of protons in an atom
- the net charge of an atoms will be zero since the protons balance out the electrons
- atoms can gain or lose an electron are called ions. Ions have a net charge that is positive or
negative but not 0.
- THE NUMBER OF PROTONS FOR EACH ELEMENT IN THE PERIODIC TABLE IS
DIFFERENT – you figure out which element you have by the number of protons that it has
- Atomic number – number of protons in the nucleus of the atom
- since an atom has the same number of electrons as protons, this is also the number of electrons
in the atom
- isotopes are atoms that have the same number of protons but different numbers of neutrons in the
nucleus
- example: chlorine has 17 protons, some have 18 neutrons and some have 20 neutrons
- some elements have many isotopes and others have just a few
- Mass number – the total number of protons and neutrons in an atoms nucleus
- different isotopes of the same element have different mass numbers since they have different
numbers of neutrons
- nucleons – name for any particles found in the nucleus – the protons and neutrons – these combined
give the mass number
Lesson 2 The Periodic Table
Essential Question: How are elements arranged on the periodic table?
By the end of this lesson, you should be able to describe the relationship between the arrangement of
elements on the periodic table and the properties of those elements.
Periodic Table over time
- Periodic Table
- First created by Russian chemist Dmitri Mendeleev
- elements are arranged by increasing atomic mass and have a regular and repeating
pattern of properties
- Mendeleev’s first version of the periodic table was a list of the elements, like the picture
on the bottom left, with question marks for where he knew elements would be but
haven’t been found yet
- Mendeleev used this repeating pattern of properties to predict elements that haven’t been
found yet
- Mendeleev then arranged his periodic table into a chart to show the patterns for where
elements with certain chemical properties would be found, like the bottom right picture.
The elements not found yet have a “---“ in the space where they will go once found.
- In the early 1900s, British scientist Henry Moseley rearranged Mendeleev’s periodic table
- Moseley figured out the numbers of protons and arranged the elements by increasing
number of protons, or atomic number.
- This new arrangement of the periodic table makes clear the patterns among the elements.
- Organization of the squares in the periodic table:
- The atomic number of each element is written at the top of the box. – this is also the number of
electrons
- The chemical symbol of the element is written in the middle. It’s the abbreviation for the
element’s name. The first letter is always capitalized with any other letters lower case.
- The chemical name of the element is written below the symbol.
- The average mass number (protons + neutrons) is written at the bottom of the box. It’s average
atomic number of all naturally occurring isotopes of the same element. Remember, isotopes are
elements that have the same number of protons but different numbers of neutrons. The unit for
atomic mass is u.
- Organization of the Periodic Table:
- Each row of elements is called a period.
- Each column of elements is called a group or family.
- The zigzag line on the right of the periodic table separates metals from nonmetals.
- Organization of the Periodic Table in your textbook on p. 312 – 313:
- The background colors show what type of element it is:
- Metals are in blue; Metalloids are in orange; & Nonmetals are in purple
- The color of the chemical symbol tells the state of matter the element is found at room
temperature Earth:
- Symbols written in black are usually solids
- Symbols written in red are usually liquids
- Symbols written in white are usually gases.
- Elements that have their box grayed out (elements above 113) are unconfirmed. Scientists know
they exist and what properties they will have due to where they are in the periodic table but
these elements haven’t been discovered yet. Whoever discovers the element will be able to
name the element. Currently these elements have a three letter symbol but that will be changed
after they are found and the scientist names them.
- 3 Major Categories of the Periodic Table of Elements:
- Metals are elements that are shiny, and conduct heat & electricity well.
- located to the left of the zigzag line on the periodic table, except for hydrogen
- most solid at room temperature
- many malleable (can be formed into different shapes)
- some are ductile (can be made into wires)
- Nonmetals are poor conductors of heat & electricity
- located to the right of the zigzag line on the periodic table
- dull and brittle (break easily)
- Metalloids are the six elements that have some properties of metals & some properties of
nonmetals.
- found directly to the right or left of the zigzag line on the periodic table
- some used as semiconductor chips in computers
- Groups within the Periodic Table:
- Groups have similar chemical & physical properties because they have the same number of
valance electrons (electrons in the outer part of the electron cloud) – valance electrons are the
electrons that bond with other atoms – this decides the types of chemical reactions the element
can do
- Groups or families are the vertical columns from top to bottom on the periodic table
- Group 1 are the alkaline metals, have 1 valance electron, & react chemically with water
- hydrogen in this column but not considered an alkaline metal even though it does
have 1 valance electron
- Group 2 are the alkaline earth metals & have 2 valance electrons
- Group 17 (used to be called group 7) are the halogens & have 7 valance electrons. They
make salts when placed near a metal so they have the name of salt generators.
- Group 18 (used to be called group 8) are the noble gases & have 8 valance electrons so
their outer orbit in the electron cloud is completely filled up and they won’t bond easily
with other elements.
- glow brightly when an electric current is passed through them (like neon in signs)
- Periods within the Periodic Table:
- Periods are the horizontal rows of elements from left to right on the periodic table
- the physical & chemical properties of the elements in each period change in predictable
ways form one end of the period to the other.
- atom size decreases as you move from left to right
- the densities of the elements also follow a pattern with the most dense elements being in
the center of each period or row and the least dense elements being on either side of the
period or row
- The two rows at the bottom of the periodic table, the lanthanides & actinides still follow all the patterns
above and increase in atomic number as moving across the period to the right. They are placed at the
bottom of the chart to allow it to be narrower.
Lesson 3 – Electrons and Chemical Bonding
Essential Question: How do atoms interact with each other?
By the end of this lesson, you should be able to use atomic models to predict whether atoms can form
bonds.
- Chemical Bond – interaction that holds atoms or ions together
- molecule – group of atoms that are held together by chemical bonds
- substances at a higher temperature have a higher amount of thermal energy
- Chemical changes change the identity of substances.
- doesn’t create or destroy atoms
- atoms rearranged to make new substances with different chemical & physical properties
- bonds between atoms are formed or broken when atoms are rearranged
- 3 different models used to represent atoms for chemical bonding:
- electron cloud model show how electrons are found in a region around the nucleus
- helps to show the general locations of the different parts of the atom
- doesn’t show the number of electrons in the atom
- Bohr model shows the number of electrons in the atom
- electrons are shown as dots placed in rings around the nucleus
- doesn’t show the true arrangement of electrons in the atom
- each ring represents an energy level, not a physical location of electrons in the atom
- space-filled model of a molecule represents atoms as solid spheres
- the spheres don’t show the parts that make up the atoms (like nucleus, protons, electrons,
neutrons)
- shows how the atoms are connected to each other
- Valance Electrons – electrons found in the outermost energy level as shown in the Bohr model
- Different number of electrons can be in each electron shell
- 1st shell holds 2 electrons; 2nd shell holds 8 electrons, & 3rd shell hold 18 electrons
- Electrons aren’t usually added to higher energy levels without filling up the lowers ones first.
- The periodic table shows the number of valance electrons in each element without having to use
the Bohr model
- the atomic number, listed at the top of each elements square, is the number of protons &
the number of electrons in that element
- elements in the same group (family), or vertical column, have the same number of
valence electrons
- Groups 1, 2, 13-18 have simple rules to tell you the number of valance electrons
- Group 1 has 1 valance electron & Group 2 has 2 valance electrons
- Groups 13 – 18 have the same number of valance electrons as the last digit in
their group number
- Group 13 has 3 valance electrons; Group 14 has 4 valance electrons;
Group 15 has 5 valance electrons; Group 16 has 6 valance electrons;
Group 17 has 7 valance electrons; and Group 18 has 8 valance electrons
- There is no easy way to figure out the number of valance electrons in groups 3-12.
- If the outermost shell of electrons (valance shell) is filled then those atoms don’t bond
easily since they already have a filled electron shell. They don’t need to give/receive
electrons or share electrons to get a filled outer shell.
- Atoms form bond to fill up the outermost electron shell. Atoms with fewer than 8 valance electrons
will gain, lose, or share valence electrons to fill up their outermost shell and become stable.
- The chlorine atom has 7 valence electrons and the sodium atom has 1. When the sodium atom gives it’s
1 valence electron to the chlorine atom, both atoms have a full outermost electron shell and have
become balanced.
- Because the sodium atom gave away an electron, it is now has a positive charge and becomes an ion of
sodium because it gave away an electron when chemically bonding.
- Because the chlorine atom accepted an electron it now has a negative charge and becomes an ion of
chlorine when it accepted an electron when chemically bonding.
- Octet Rule – All atoms need 8 electrons in their outermost shell (valence) in order to be stable. Atoms
will share, steal, or give away electrons in order to have 8.
Lesson 4 – Ionic, Covalent, and Metallic Bonding
Essential Question: How can atoms join together?
By the end of this lesson, you should be able to describe the interactions between atoms in ionic, covalent,
and metallic bonding.
- Ion - an atom that has a positive charge because it gave away electrons or a negative charge because it
accepted electrons when chemically bonding.
- Chemical bonds hold two or more atoms or ions together. Remember the Octet Rule for bonding!
- Ionic bond – is a force that brings oppositely charged ions together.
- form when electrons are transferred from a metal atom to a nonmetal atom
- valence electrons move from the outermost energy level of the metal atom to the
outermost energy level of the nonmetal atom.
- the movement of the electron fills up the outermost energy level and creates a stable
compound
- Properties of most ionic compounds:
- Have a neutral charge since the number of electrons lost by the metal atom is equal to the
number of electrons gained by the nonmetal atom.
- Crystal lattice structure – form repeating three-dimensional (3-D) patterns.
- High melting & boiling points since it takes a lot of energy to separate the ionic bonds
- Hard & Brittle – more likely to break than bend – if hit by a hammer it will shatter into
many pieces
- Electrical Conductivity – will carry an electric current
- Solid ionic compounds won’t conduct electricity - ions held tightly in place
- Melted ionic compounds are liquids and the ions can move around some, this
allows them to conduct electricity
- Ionic compounds dissolved in water also conduct an electric current
- Solubility in water – ability to dissolved in water
- water separates the ions from each other and dissolve them
- Covalent bond – forms when atoms share one or more pairs of electrons
- most compounds have this type of bond
- happens with two nonmetals bond
- in covalent bonds, atoms can share 1 electron, 2 electron, or 3 electrons to fill up their
outermost electron shell and become stable
- Molecule – group of atoms held together by covalent chemical bonds.
- Covalent compounds are molecules that have atoms of more than one element
- Properties of Covalent Compounds:
- The covalent bonds that hold the atoms together are strong but the force holding the
molecules to one another are week
- Low solubility in water – many will hold closer together to each other and will not break
apart in water although a few are soluble in water
- Low melting and boiling point – the bonds holding the molecules together don’t break
apart, the molecules separate from each other instead
- Poor Electrical Conductivity – poor conductors of electric currents as both solid & liquid
- the molecules are neutral so they don’t move around, even in liquid form & don’t
conduct an electric current
- the few covalent compounds that dissolve in water do conduct an electric current
since water has broken them up into ions
- Metallic Bond – forms between metal atoms when their outermost energy levels overlap
- weak compared to ionic or covalent bonding
- positively charged metal ions form when metal atoms temporarily lose electrons – the
positive ions are held together in a crystal structure and don’t move
- electrons move freely in all directions throughout the overlapping outermost energy
levels of all the bonded metals
- the moving electrons keep the shape of the metallic bonds when the metal is pounded
into a different shape – this allows metals to bend without breaking
- Properties of most Metallic Compounds:
- Good Electrical Conductors because the electrons can move around freely
- Malleable – can be hammered into sheets because the free flowing electrons hold the
metal together
- Ductile – can be formed into long, thin wires also because the free flowing electrons hold
the metal together
- Lewis Dot Structure is used to show the bonds between atoms.
- Write the chemical symbol
- Figure out the number of valance electrons & position them around the sides of the chemical
symbol
- Put one in each of the sides first, then go back and fill in a second on each side.
- DO NOT put three on any side of the symbol