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Atomic Structure
Elements
All elements are composed of only one type of atom. In these atoms are three subatomic particles:ProtonsNeutronsElectrons
Elements
-Protons have a positive charge (+)-Neutrons have no charge (neutral)-Electrons Have a negative charge (-)
• Most of the mass of an atom is found in the nucleus which contains the neutrons and protons.
Atomic number
• Atomic number tells you how many protons that elements has.
• If the number of protons changes, the element changes.
Atomic number
• Since the atom of an element is neutral, then the atomic number also tells you how many electrons you have.
Atomic # = # of protons = # of electrons
Atomic Mass
• Atomic mass is the total number of protons and neutrons found in the nucleus of an atom.
• # of protons + #of neutrons = atomic mass
Neutrons
• To find out how many neutrons and element has:
a) Round atomic mass to nearest whole numberb) Subtract atomic number from atomic mass to
get number of neutrons
Atomic Mass – Atomic Number = # of neutrons
Example
• Na (sodium)• Atomic mass is 22.989• Atomic mass rounded 23• Atomic number is 11Atomic Mass – Atomic Number = # of neutrons• 23-11= 12• Na has 12 neutrons.
Try these!!!
Co (Cobalt)
• Atomic mass is 58.933
• Atomic mass rounded 59
• Atomic number 27• 59-27= 32
Ag (Silver)
• Atomic mass is 107.868
• Atomic mass rounded 108
• Atomic number 47• 108-47 = 61.
Bohr’s model
• Is a physical drawing that shows where all the subatomic particles are located in a particular atom of an element.
• The Bohr’s model is similar to our very own solar system.
Bohr’s Model
• Protons and neutron are always found in the nucleus of the atom of an element.
• Electrons are around the atom in an area called the electron cloud.
• In this electron cloud are orbitals where electrons move around the nucleus of the atom.
Bohr’s Model
• Each orbital can only hold a certain amount of electrons:
• 1st orbital- 2 electrons• 2nd orbital- 8 electrons• 3rd orbital- 8 electrons• 4th orbital- 18 electrons
• The elements found in a group have similar properties because they have the same number of valence electrons.
• The horizontal rows on the periodic table are called a period. Periods tell you how many orbitals will be on your drawing.
• Ex. Na (sodium) is in Period 3, it will have 3 orbitals in its Bohr’s Model.
• The vertical columns on the periodic table are called groups. Groups tell you how many valence electrons the element has.
• Ex. Na (sodium) is in Group 1 so it has 1 valence electron.
• Valence electrons are the electrons that occupy the last orbital of an element.
• Orbitals are also called energy levels.
Boron (B)
5 p+
6 n
Al
13 p+
14 n
Lewis-Dot Structure
• The amount of dots you draw for a Lewis Structure (LS for short) is equal to the # of Valence Electrons in an Atom
Valence Electrons
• The # of Valence e- an atom has is dictated by the Group that the Element is in• Groups are the Vertical
Columns on the Periodic Table!!! It’s So Simple!!!!
• Isotopes are atoms of a given element that have different numbers of neutrons and different mass numbers.
• Ex. Oxygen-16; has 8 neutrons Oxygen-17; has 9 neutrons
Oxygen-18; has 10 neutrons
These are all still oxygen atoms.
• Elements on the periodic table are classified as one of the following:
• Metals• Nonmetals• Metalloids