Atoms, Molecules and Ions H.Imam Rachmat,spd

Objectives To 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 matter Look at the figure ! On 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

What is an atom??? Atom is the smallest unit of an element, having the properties of that element. Democritus’s model ( the father of atomic theory) Fe Fe Fe Fe Fe Fe Fe This is atom Fe ( iron )

How has the model of the atom changed over time ? Dalton’s Concept 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: Matter is made up of atoms, Atoms cannot be divided into smaller pieces, All the atoms of an element are exactly alike Different elements are made of different kinds of atoms. Dalton’s model 1807

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- nucleus e- e-

Structure of atoms THE STRUCTURE OF ATOMS Atoms are made up of three subatomic particles Protons carry positive charge Neutrons having no charge Electrons 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 charge Position in atom Proton Neutron electron +1 No charge - 1 Atom nucleus Moving around atom nucleus

Atomic Mass

ISOTOPES Isotopes are atoms with the same atomic numbers but different mass numbers. EXAMPLES Hydrogen Chlorine Carbon

ISOBAR Atoms of different elements might have the same mass number. EXAMPLES ISOTONES Atoms of different elements might have the same number of neutron EXAMPLES

Electron Arrangement According 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 arrangement Sodium Σp=11 Σe=11 Σn=12 Electronic Configuration: 2, 8, 1 1st shell 2nd shell 3rd 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

ions Ion is an atom having electric charge When atoms lose or gain electrons, they become ions atom Loses electrons + Positive ion _ Negative ion An atom may gain or lose electrons Gains electrons

Cl Na+ Na Cl- cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. Na 11 protons 11 electrons Na+ 11 protons 10 electrons anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. Cl 17 protons 17 electrons Cl- 17 protons 18 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 Na+, Cl-, Ca2+, O2-, Al3+, N3- A polyatomic ion contains more than one atom OH-, CN-, NH4+, NO3- 2.5

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. + 

BaCl2 barium chloride K2O potassium oxide Mg(OH)2 magnesium hydroxide 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

Example:   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 compound Ionic 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. Molecule A 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