General Chemistry

Faculty of Allied Medical Sciences

(MGGC-101)

Supervision:Prof.Dr.Shehata El-Sewedy

Dr.Fatma Ahmed

Atoms, molecules and ions

Outcomes By the end of this lecture, the

students will be able to1-Recognize the significant figures in

measurements2-To differentiate between International System of

Units 3-To know Dalton’s atomic theory

4-Understand Atomic number, Mass number and Isotopes

5-Know the meaning of molecule and its types6-learn to the meaning of ion and its types

3. Significant figures in measurementsIn any measurement, there is always a degree

on uncertaintyRules to determine the number of significant figures ►The numbers recorded in a measurement are called significant digits or significant numbers. 1. Digits other than a zero are always significant. 854 ► 3 sig figures and 3.6 ► 2 sig figures2- Zeros between non-zero digits are Significant. ► 4 sig figures and 30.76 ► 4 sig figures3- Zeros at the beginning of number are not significant. 012 ► 2 sig.fig. and 0.012 ► 2 sig.fig4- Zeros at the end of number and after the decimal point are Significant. 19.60 ► 4 sig figures5- Zeros at the end without decimal point May or may not be significant. (Use exponential notation).Example: 500 could have 3 sig figures ► 5.00 X 102 or have 2 sig figures ► 5.0 X 102 or have 1sig figure ► 5 X 102

Example

Significant figures in calculations1- In multiplication and division The result must have the same number of S.F. as the number having the least S. F. in the calculation. e.g. 7.5023 2.00 = 15.0046 wrong

5 S.F. 3 S.F 15.0 (only 3 S.F. Correct

34.103 0.0310 = 10.57193 wrong

10.6 (only 3 S.F.) correct

2- In addition and subtraction The result must have the same number of decimal digits as the number with the least decimal digits in calculation. e.g. 25.23 + 21.3207 = 46.5507

2 d.d. 4 d.d 46.55 (only 2 decimals)

10.31 + 0.002438 = 10.307562

10.31 (only 2 decimals)

RoundingLook at the leftmost digit to be dropped, then1-If this digit is greater than 5, add 1 to the last digit to be retained. Thus, rounding 1.2161 to 3 significant figures gives 1.22.2-If digit is less than five, drop it, Thus, rounding 1.2141 to 3 significant figures gives 1.21.3-If this digit is 5 : 15.55 = 15.6 odd 15.45 = 15.4 even

Example:Perform the following calculations and round the answers to the correct number of significant figures:a.

b.

c.

d. 37.76 + 3.907 + 226.4  

Solution:The factor 5.8 has the fewest significant figures; therefore the answer should be reported to two significant figures. Round the answer to 3.6

The number with the least number of decimal places is 5.41. Therefore, round the answer to two decimal places, to 5.01

The answer is 0.37. Note how you have lost one significant figure in the subtraction.

The answer is 268.1

Units of measurement Measurement always consists of two parts, a number and a unit. •1-Metric system

2- International System of Units (SI system)This system is commonly used in all countries.Fundamental SI units

Some unit conversations:1 kilogram = 1 103 gram 1 megagram = 1 106 gram 60 second = 60 1015 femto second

Femto second = 1 10–15 second Pico meter = 1 10–12 meter 1 meter = 1 1012 pico meter

Derived SI units Units which are not fundamental SI units called derived. Area = (Length)2

Volume = (Length)3

Liter = 103 cm3 = 103 mL Velocity = m/s (length/time) Density = g/cm3 (mass/volume)

DALTON’S ATOMIC THEORY (1808)

1-Elements are composed of extremely small particles called atoms .

2-All atoms of a given element are identical, having the same size, mass and chemical properties. The atoms of one element are different from the atoms of all other elements.

Atoms, molecules and ions

3 -Compounds are composed of atoms of more than one element. In any compound, the ratio of the numbers of atoms of any two of the elements present is either an integer or a simple fraction.

4 -A chemical reaction involves only the separation, combination, or rearrangement of atoms

8 X2Y16 X 8 Y+

SUBATOMIC PARTICLES

Particle Symbol Charge Mass

Electron e- - 9.11X10-28 g

Proton p+ + 1.67X10-24 g

Neutron n 0 1.67X10-24 g

An atom is neutral The net charge is zeroNumber of protons = Number of electronsAtomic number = Number of electrons

Atomic number and Mass number

Atomic number (Z) = number of protons in nucleus

Mass number (A) = number of protons + number of neutrons

= atomic number (Z) + number of neutrons

XA

Z

Mass Number

Atomic NumberElement Symbol

163165 O P Zn 81530

8 p+15 p+30 p+

8 n16 n35 n8 e-15 e-30 e-

SUBATOMIC PARTICLES IN SOME ATOMS

Isotopes:The isotopes of an element have the same atomic no. (same chemical properties) but differ in their mass no. (different physical properties) i.e they have same no. of protons but different no. of neutrons.Example: the isotopes of hydrogen

Eg. 12C, 13CThe 2 atoms have the same at.no. (equal no. of protons)But they differ in their mass no. (different no. of neutrons) 12C: at.no.= 6,mass no.=12, no. of neutrons=6 13C: at. no. =6, mass no.=13, no. of neutrons=7Eg. O atom 16O, 17O, 18O 8p, 8p, 8p 8n, 9n, 10n 8e, 8e, 8e

A molecule is an aggregate of two or more atoms held together by chemical forces

H2 H2O NH3 CH4

A diatomic molecule contains only two atomsH2, N2, O2, Br2, HCl, CO

A polyatomic molecule contains more than two atoms

O3, H2O, NH3, CH4

Molecules and Ions

The forces that hold atoms together in molecules are called chemical bonds .

Molecules can be represented in several different ways: Chemical formulaRepresent the type and actual number of atoms in a molecule ,

for example, carbon dioxide CO2 (it has 1 carbon atom and 2 oxygen atoms) .

Structral formulaFormula by which the individual bonds are shown (may or may not show the actual shape of molecule).Example

IonsAn ion is an atom, or group of atoms, that has a net positive or negative charge. An ion may be a cation or an anion.Cation: ion with a positive charge. If a neutral atom loses one or more electrons it becomes a cation.

Anion: ion with a negative charge. If a neutral atom gains one or more electrons it becomes an anion.

Quiz time

What is the number of protons and electrons in S2–

What is the number of protons and electrons in aluminum ion, Al3+

16O, 17O, 18O

What is the number of protons, neutron and electrons in

How many Significant figures and decimal points in

Student Question

What the SI units of1-time 2-length 3-temperature4-amount of substance 5-mass 

 Answer the following operation18.5+31.3=3.2+5.09+3.007=36.36÷4.04=4.053÷4.00=27.00x2.00=0.0040x3001.37= 

How many Significant figures in 1)32.01 2)5.010 3)32.00 4)200 5)8.1

Calculate the no. of proton, neutron and electrons for

Cl35

17 , Ni+459

28

Define and give example:

CationAnionIsotopeStructural formula

AssignmentsGroup A and Group B

Aya Salah- Omnia Gamal- Hanan Farg-Sarah Fasal Hashem

Types of Ions

Saad Mohamad El-sawiMohamad Ahmad FouadMohamad MoawadEl hussein Mohsen -Adel AhmedMahmoud Abd El- Mageed

Uses of cations in industry

Mana Allah Gamal- Malak Atef-Yasmine Abd ElHameed

Applications of Isotopes

Ali Hasan – Mahmoud Mohamad- Amir Mohamad- Mervat Abd El-Halim- Mervat Essam – Yasmine Rabee

Applications of anions

RECOMMENDED TEXTBOOKS:

1-Raymond Chang. Chemistry. 10th ed. 20092-Zumdehl. International edition. 2009