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STRUCTURE
OF
MATTER
Each element is made up of very small units of matter called
“Atoms”
Atom
-
-
the basic structural unit of an element
the smallest portion of an element that retains all the properties of that element
- Made up of 2 general areas
1) Nucleus
- a solid core
2) Orbits or Shells
- the area outside the nucleus where the electrons are found
- both of these areas are then made up of subatomic particles
- a very dense, small, positively-charged center of an atom that contains most of the atom in the form of protons and neutrons
Subatomic Particles
Protons
- positively charged particles found in the nucleus of an atom
- mass of 1 amu
- charge of +1
1)
2)
- uncharged particles found in the nucleus of an atom
- mass of 1 amu
- no charge (neutral)
Neutrons
3)
- negatively charged particles found in the shells or orbits surrounding the nucleus
- mass of 1/1837 amu
- we will consider it to be 0
- has a charge of -1
Electrons
Other Atomic Theory Terminology:
Atomic Number or Element Number
-
-
the number of protons in the nucleus of an atom
OR
the number of electrons in the shells of an uncombined atom
Other Atomic Theory Terminology:
Atomic Weight
-
- Defined as:
the weight of a given atom
- the sum of the weights of the electrons, protons, and neutrons
Arrangement of the Electrons in the Atom
- the electrons are always found arranged in a particular order around the nucleus of an atom
- this order is called the electronic configuration
- each shell or energy level can contain only a certain number of electrons
- The first energy level must be completely filled before electrons may fill the second energy level and so forth
- the most electrons that can be found in the outermost shell is 8 for those atoms that we are concerned with
- those electrons found in the outer-most shell of an atom are called valence electrons
- they are also the particles that will actually be combining with like particles of another atom to bond the atoms together and form a compound
these electrons are responsible for the chemical properties of the element
THE PERIODIC TABLE
OF THE
ELEMENTS
1 2 3 4 5 6 7 8
Developed to attempt to group the elements according to similar properties and types of reactions
- the elements are arranged horizontally(in rows) in order of increasing atomic number
1
2
3
4
5
6
7
PERIODS
1 2 3 4 5 6 7 8
- the elements are also grouped together vertically(in columns) according to their similar chemical properties
- these are called Groups or Families
1 2 GROUPS 3 4 5 6 7 8
- each member of a group is “related” to the other members because:
1)
2)
they have similar chemical properties
they have the same number of valence electrons *******
- only the electrons in the outermost shell(valence electrons) react with the electrons of other atoms…
Groups With Special Names
- Group 1 Alkalis
- Group 7 Halogens (salt-formers)
- Group 8 Inert Gases or Noble Gases
- Inert means “will not react”
1 2 3 4 5 6 7 8
NOBLE OR INERT GASES
HALOGENS
ALKALIS
MOLECULES
Remember
The atomic symbol not only identifies an element but it also represents one atom of that element
For example:
- the symbol Cu represents the element copper as well as one atom of copper
- two individual or uncombined atoms of copper would be written as
- 2Cu -- three as 3Cu, etc
- Cu2 represents one molecule of copper which consists of 2 atoms of copper that are chemically combined
- two molecules of copper would be written as 2Cu2
A molecule is defined as
- as in HCl or NaCl
- or they could be atoms of different elements that form a compound
- as in O2
- these could be atoms of the same element
- a combination of two or more atoms
Some elements as found in nature will form molecules with themselves in order to be stable
Such as oxygen…..
- you will never find oxygen in nature as just one atom of oxygen
- it can only be found as O2 (or two atoms of oxygen combined together)
- the same goes for hydrogen (H2), chlorine (Cl2) and nitrogen (N2)
- the atoms are held together in a molecule by two types of chemical bonds that we will discuss later
- these types of elements are considered to be ….diatomic
- only the noble gases can stand on their own as monatomic atoms
A formula is defined as
Formula
- a group of symbols that represents all the elements present in a compound or molecule
- the formula NaCl says that the compound sodium chloride contains one atom of sodium (Na) and one atom of chlorine (Cl)
- if there is more than one atom of an element present in a compound, subscripts are used to show how many atoms there are
For example in:
- HNO3 (nitric acid) there is …
- one atom of hydrogen
- one atom of nitrogen
- three atoms of oxygen
- these atoms all together make up one molecule of the compound HNO3
- two molecules would be shown with a coefficient as in
- 2HNO3
IONS
- An ion is defined as
- a “charged” atom
- it has either a positive or negative charge
- how does it get this charge???
- the atom must have either lost or gained electrons
1) Cation
- an atom that has lost electrons
- when an atom loses electrons it becomes positively charged
There are three types of ions:
2) Anion
- an atom that has gained electrons
- when an atom gains electrons it becomes negatively charged
3) Polyatomic ion or Radical
- a charged group of atoms that stay together and act as a single unit in chemical reactions
- Required Radicals:
Ammonium NH4 Sulfate SO4
Hydroxide OH Sulfite SO3
Nitrate NO3 Phosphate PO4
Nitrite NO2 Phosphite PO3
- when ions are formed, they take on the electronic configuration of an Inert Gas
- atoms are always “striving” to achieve a full outermost shell so they will lose or gain electrons to do this
ELECTRON DOT
OR LEWIS DOT STRUCTURE
- an abbreviated representation for the structure of an atom
- the symbol stands for the nucleus and all of the energy levels except for the outermost
- the dots stand for the valence electrons
Na or Cl
•
•
•
•
•
•
•
•
Tying this to IONS……
Consider the Na atom again
*- because it is in Group I
- it has one valence electron
- in order to gain stability, it will
- tend to lose this electron
- to achieve a full outermost shell of eight electrons
- Na normally has 11 protons and 11 electrons
- when it loses one electron it leaves an overbalance of 11 protons and 10 electrons
- therefore it is a positively charged particle…….
an ion
- most specifically a cation
Consider the Cl atom again
*- because it is in Group VII
- it has seven valence electrons
- in order to gain stability, it will
- tend to gain an electron
- to reach a full outermost shell of eight electrons
- Cl normally has 17 protons and 17 electrons
- when it gains one electron it leaves an overbalance of 17 protons and 18 electrons
- therefore it is a negatively charged particle……..
an ion
- most specifically an anion