Download Writing and Naming Chemical Formulas

Ms. Grobsky
A Summary of Atomic
Structure

 The atom consists of positive, negative, and neutral entities called protons,
electrons, and neutrons
 Protons determine element’s identity
 # of protons is unique for each element
 Electrons determine element’s chemical properties
 Neutrons act as a “glue” for the protons to minimize charge repulsions
 Protons and neutrons are located in the nucleus of the atom, which is small
 Therefore, the nucleus is positively-charged
 Although small, most of the mass of the atom is due to the nucleus
 Electrons are located outside of the nucleus at an average distance of 10-8
cm
 Therefore, the electron cloud is negatively-charged
 Most of the volume of the atom is due to electrons
Nucleus Size vs. Electron
Cloud Size

Masses of the Proton,
Neutron, Electron

Element Symbols, Atomic Number, and Mass
Number

 Atomic number (Z)
 Represents the number of protons in the nucleus
 Mass number (A)
 Represents the total number of nucleons in the nucleus (i.e.,
protons and neutrons)
Mass Number = # of protons + # of neutrons
 Mass number is NOT the number on the Periodic Table
 Although numerically similar, this is the average atomic mass –
more on this later!
Isotopes

 There can be a variable number of neutrons for the
same number of protons
 Isotopes have the same number of protons but
different numbers of neutrons
 “Different” versions of the same element
 Masses are different due to the different number of
neutrons
 So, isotopes have the same Z but different A!
Isotopes of Carbon

An Element’s Charge

 All elements on the periodic table are electrically
neutral
 Positive charge of the protons equals negative charge
of the electrons
 In order for an element to be neutral, the number of
protons must equal the number of electrons
 Atomic number equals number of electrons!
Calculating # of Protons,
Electrons, and Neutrons

Atomic #
Na
Hg
Mass #
# of P+
# of N
# of E-
The Elements and the
Periodic Table

 The Periodic Table is used to organize the 114
elements in a meaningful way
 Arranged by increasing atomic number
Organization of the Periodic Table

 Columns in the periodic table are called groups
 Numbered from 1 to 18
 Atoms with similar properties appear in groups
 They are similar because they all have the same number of
valence (outer shell) electrons, which governs their chemical
behavior
 Group numbers represent the number of valence electrons
 Group 1 has 1 valence electron
 Group 2 has 2 valence electrons
 Groups 13 – 18 must subtract 10 to get # of valence electrons
Families of the Periodic
Table

 Some of the groups in the periodic table are
given special names, and are called families
 These names indicate the similarities of chemical
properties between group members as a result of
same number of valence electrons:





Group 1:Alkali metals
Group 2: Alkaline earth metals
Groups 3-12: Transition Metals
Group 17: Halogens
Group 18: Noble gases
Organization of the
Periodic Table

 Rows in the periodic table are called periods
 Numbered from 1 to 7
 Elements of the same period have the same number
of energy levels
 As you move across a period, the number of
electrons and protons increases, leading to
increase in atomic number
 Elements within the same period do not
generally show similarity in properties, except dblock and f-block (lanthanides) elements
Review of the Periodic Table

Organization of the
Periodic Table

 Metals are located on the left hand side of the
Periodic Table
 Most of the elements are metals
 Non-metals are located in the top right hand side of
the Periodic Table
 Elements with properties similar to both metals and
non-metals are called metalloids and are located at
the interface between the metals and non-metals
Non-metals above
the staircase
Metals below the
staircase
Properties of Metals and Non-Metals

Metals
 Shiny
 All but gold and copper
are silver or grey in
color
 Conduct electricity
 Ductile
 Malleable
 Lose electrons
Non-metals
 Not shiny
 Most are colored
 Do not conduct
electricity
 Not malleable
 Gain electrons
Metals

Non-Metals

More About the
Elements

 Some elements are found in nature in their elemental
form
 Most elements combine naturally with each other to
become more energy-stable materials
 Atoms of an element gain, lose, or share valence
electrons with other atoms to become chemically
stable
 Atoms of elements are not chemically stable until
they have 8 electrons (octet rule)
 Hydrogen is an exception – only needs 2 electrons!
Formation of
Positive Ions

When an atom or molecule loses electrons, it
becomes positively charged
For example, when Na loses an electron it
becomes Na+
Positively charged ions are called cations
Formation of Negative
Ions

 When an atom or molecule gains electrons, it becomes
negatively charged
 For example when Cl gains an electron it becomes Cl Negatively charged ions are called anions
 An atom / molecule can lose or gain more than 1
electron!

Oxidation Numbers

 Defined as the overall charge of an ion after it has
lost or gained electrons
 Metals lose electrons, so they form cations
 Non-metals gain electrons, so they form anions
 Can be determined by looking at the Periodic Table
 Since ions are formed by losing or gaining valence
electrons, the group number also represents the charge
the elements in that group like to form!
Predicting
Oxidation Numbers
