Atoms, Molecules and Ions
Grade VIII Semester 12010/2011
Abdul Malik SRJunior High School 1 Lamongan
ObjectivesTo define the meaning of particles of matter (atom, ion and molecule)
To explain the difference of isotope, isotones and isobar
To explain the difference between the element molecule and the compound molecule
To mention some examples of simple molecules in daily life
To give examples of substances that consist of ions
PARTICLES OF MATTEROn grade VII you learned that all matters around us are made up of
fundamental matter called ELEMENT.
Element is a simple substance whch cannot be broken down into simpler subtances
Look at the figure !
A piece of iron is composed of a mass of iron atoms
A piece of iron
Iron atom
What is an atom???Atom is the smallest unit of an element, having the properties of that element.
This is atom Fe ( iron )
Fe
Democritus’s model
( the father of atomic theory)
Fe Fe
Fe Fe
Fe Fe
How has the model of the atom changed over time ?
Dalton’s Concept
DALTON’S MODEL 1807
John Dalton, an English schoolteacher in the early nineteenth century, combined the idea of elements with the earlier theory of the atom. He proposed the following ideas about matter: (1)Matter is made up of atoms, (2)Atoms cannot be divided into smaller pieces, (3)All the atoms of an element are exactly alike(4)Different elements are made of different kinds of
atoms.
Thomson’s model 1903
Atom is continuous
mass of positive
charge containing
negative electron
Raisin pudding model
Rutherford’s model 1903
Atom has a nucleus
surrounded by
electron
e- e- e-
e-
e- e-
e-
e-
e-
Niels Bohr’s model 1913
Atom has a nucleus.
Electrons move
in fixed orbits
around the
nucleus
e-
e-
e-
nucleus
Structure of atomsTHE STRUCTURE OF ATOMS
• Atoms are made up of three subatomic particles
Protons carry positive chargeNeutrons having no chargeElectrons carry negative charge
• The protons and neutrons are tightly bound together to form the central portion of an atom called the nucleus.
• The electrons are located outside of the nucleus and thought to move very rapidly throughout a relatively large volume of space surrounding the small but very heavy nucleus.
The comparison of particles in atom
particles charge Position in atom
ProtonNeutronelectron
+1No charge- 1
Atom nucleusAtom nucleusMoving around atom nucleus
ATOMIC MASS
ISOTOPESIsotopes are atoms with the same atomic numbers but different mass numbers.
EXAMPLES
Hydrogen
Chlorine
Carbon
ISOBARAtoms of different elements might have the same
mass number.
EXAMPLES
ISOTONESAtoms of different elements might have the same
number of neutron
EXAMPLES
Electron ArrangementAccording to Bohr, electrons move around the nucleus in fixed orbit or shells
The electron in each shell have different energy level. The shells closes to the nucleus have lower energy levels than those farther away
The biggest atoms can have up to 7 electron shells,
However, each shell can contain only a limited number of electrons. This number depends on their size:
1st shell maximum filled with 2 electrons.
2nd shell maximum filled with 8 electrons.
3rd shell can hold up to 18 electrons, but normally only holds up to 8 to make atom more stable.
4th shell can hold up to 32 electrons but, like the third shell, normally holds only up to 8 to make atom more stable
Example of Electron arrangementSodium Σp=11
Σe=11
Σn=12
Electronic Configuration: 2, 8, 1 1st shell
2nd shell3rd shell
Electronic Structure
The electron in the outermost shell of an atom are called the outer electron or valency electrons
Sodium has 1 valency electron
When atoms lose or gain electrons, they become ions
IONSIon is an atom having electric charge
atom
Loses electrons
+Positive ion
_ Negative ion
An atom may gain or lose electrons
Gains electrons
cation – ion with a positive chargeIf a neutral atom loses one or more
electrons it becomes a cation.
anion – ion with a negative chargeIf a neutral atom gains one or more
electrons it becomes an anion.
Na11 protons11 electrons Na+ 11 protons
10 electrons
Cl17 protons17 electrons Cl-
17 protons18 electrons
Predicting Ionic Charge• Metals tend to form cations (group 1 and 2)• Non-metals tend to form anions.(group 5, 6, 7 )
Be2+
A monatomic ion contains only one atom
A polyatomic ion contains more than one atom
2.5
Na+, Cl-, Ca2+, O2-, Al3+, N3-
OH-, CN-, NH4+, NO3
-
1. Why do atoms bond together?
Atoms bond to become more stable, like Noble Gases.
1. Ionic bonds Ionic bonds are formed by one atom transferring electrons to another atom to form ions.
Ionic Compound – A compound that contains positively charged ions and negatively charged ions.
+
Ionic Compounds
often a metal + nonmetal
anion (nonmetal), add “ide” to element name
BaCl2 barium chloride
K2O potassium oxide
Mg(OH)2 magnesium hydroxide
KNO3 potassium nitrate
2.7
2. Covalent Bonding Covalent bonds are formed by atoms
sharing electrons to form molecules. This type of bond usually formed
between two non-metallic elements.(between 2 gass)
Example:Two hydrogen atoms (1) form the molecule of the element hydrogen H2
Two chlorine atoms (2.8.7) form the molecule of the element chlorine Cl2
+
+
Another examples of covalent bond:
Oxygen (o2)
Water (H2O)
Ammonia (NH3)
Carbon Dioxide (CO2)
Comparison properties of ionic and covalent
compoundIonic Compound
Covalent Compound
Electrical Conductivity
Conduct electricity when dissolved in water
Does not conduct electricity in any state
Melting point and boiling point
High Low
Solubility in water
Mostly soluble Mostly insoluble
C. MoleculeA molecule is made up of two or more atoms chemically combined together.
Molecules of Element
• Molecules are made up of the same kinds of atoms
Molecules of Compounds
• Molecules are made up of two or more different kinds of atoms
MOLECULES OF ELEMENT
MOLECULES OF COMPOUND
The using of ions and molecules in chemical product in daily life
Composer Product
Polyvinyl Chloride (PVC)
Water pipe, tile
Polyetilene Carpet, laboratory apparatus
Isoprene (C5H8) and polystyrene
Rubber
Sucrose (C12H22O11) Sugar, Syrup
Ionic compound NaCl
Table salt
Ion-ion (Cl-, Na+,Mg 3+, Ca2+)
Isotonic drinks
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