1-21-2 The Simplest The Simplest MatterMatter

An element is a matter made of atoms of only one kind.

I. The ElementsI. The Elements

eg: the gold coin is an element made of gold atoms.

Iron nail is an element made of iron atoms.

Statue of Liberty is made of copper atoms.

Diamond is made of carbon atoms.

Other matter are made of atoms of more than one kind, they can be taken apart into different kinds of atoms by proper equipments.

eg: water can be taken apart into hydrogen and oxygen gas.

H2O H2 + O2

C S H N O

DNA——the biomolecule that stores the genetic information of living things is made up of five different elements.

At this time, 115 elements are known.Everything on Earth is made up by the elements or combination of these elements.

• http://www.webelements.com/

90 of them are naturally occurring elements.

eg: element hydrogen and oxygen can be found in water.

eg: element carbon, nitrogen, hydrogen, oxygen, iron…can be found in a puppy.

25 of them are synthetic elements.

Made by scientists with machines.

Synthetic elements are marked with a bull’s-eye logo.

new synthetic element

Fermilab spans 6200 acres of land, just enough area to accelerate particles close to the speed of light. The particle accelerator, the Tevatron is located inside the large circle on the photo.

Dewey Decimal Classification system helps you find a book quickly and efficiently.

II. The Periodic TableII. The Periodic Table

Periodic table is a chart of elements to help chemists to organize and display the elements.

Periodic table

Element symbol is a shorthand that chemists use to save time and space.

Eg: H is the symbol for hydrogen.

O is the symbol for oxygen.

The rows in the table are called periods.The elements in a row have the same number of energy levels.

period

The columns in the table are called groupsThe elements in a group have similar properties.

group

III. Identifying CharacteristicsIII. Identifying Characteristics

Proton

Neutron

Nucleus

Electron

The number of electrons equals to the number of protons.

All the atoms of an element are exactly alike. Different elements are made of different kinds of atoms.

All the atoms of an element have the same number of protons.

The atoms of different elements have different number of protons.

eg: The oxygen atoms in water, air or plants all contain 8 protons in their nucleus.

eg: iron atoms all contain 26 protons in their nucleus.

The number of protons in the atom of the element equals to atomic number.

Ex: how many protons in the atoms of the following elements?

(a)Carbon (2nd period, 14th group)

(b)Sodium (3rd period, 1st group)

(c)Radon (6th period, 18th group)

Answer:(a) 6(b) 11(c) 86

For one element, the number of neutrons can be different.

eg: all atoms of H element contain 1 proton in the nucleus.Some H atoms contain no neutron while others contain 1 or 2 neutrons in their nucleus.

Atoms of the same element that have different numbers of neutrons are called isotopes.

An atom’s mass number is the number of protons plus the number of neutrons it contains.

Isotope of hydrogen

protium deuterium tritium

Proton

Neutron

Mass Number

mass number = nproton+ nneutron

Isotope of oxygen

1 2 3

Proton 8

Neutron 7 8 9

Mass Number

ex 1: Oxygen have three types of atoms which contain 7, 8, 9 neutrons respectively.

Different isotopes of the element are referred to using its mass number.Eg: O-15, O-16, O-17

• Quiz: element 1-20

• Symbol, name, atomic number.

Isotope of chlorine

Cl-35 Cl-37

Proton

Neutron

Mass Number

electron

ex 2: Chlorine has two isotopes Cl-35 and Cl-37. Fill the table below.

atoms

Proton

Neutron

Mass Number

electron

proton neutron electron Mass number

I 53 131

Co 33 27

Mo 56 98

U 92 143

Ba 56 141

Multiple choiceTrue or false (if it is false, correct it)Filling tables.Filling blanks. (probably)Match. Short answers.Calculation. (atomic mass )

Paper dictionary, calculator are allowed.

Atomic mass is the weighted average mass of the isotopes of an element.

Cl - 35Cl - 37

75.8%

24.2%

If you have 100 chlorine atoms, 75.8% of them are Cl-35 and 24.2% are Cl-37.What’s the atomic mass of Cl?

Atomic mass of chlorine =75.8%×34.97u+24.2%×36.97u

=35.45 u u – atomic mass unit

Chlorine17 Cl

35.453

IV. Classification of ElementsIV. Classification of Elements

Most of the elements are metals, they are found on the left side of the periodic table.

MetalloidsMetals

Three general categories of elements—— metals, metalloids and nonmetals.

nonmetals

The properties of metals:The properties of metals:

1. Most with high melting point (solid →liquid)2. Metallic luster3. Good conductor of heat and electricity4. Malleable5. Ductile

1. Metals1. Metals

Luster

Think about the uses of these properties of metal:

Good conductor of heat

Good conductor of electricity

Malleable

Ductile

The properties of nonmetals:The properties of nonmetals:

1. Usually gases or brittle solids at room temperature.

2. Dull in appearance.3. Poor conductors of heat and electricity.

2. Nonmetals2. Nonmetals

All nonmetals are gases and brittle solids at room temperature except one. Can you find this element?

bromine

Nonmetals are essential for life.

Can you find out the nonmetals in protein?

3. Metalloids3. Metalloids

Silicon are used to make the electronic circuits in electronic devices.

The elements between metals and nonmetals are metalloids (semimetals).

Metals

Nonmetals

Metalloids

Metalloids share some properties with metals and some with nonmetals.

The properties of The properties of metalloids:metalloids:

Slight luster, conduct electricity at high temperature;Brittle, does not conduct electricity at low temperature.

Oxygen is the most abundant element in Earth’s crust.

Aluminum is the most abundant metal element in Earth’s crust.

ExercisesExercises1. The nucleus of one atom contains 12 protons and

12 neutrons, while the nucleus of another atom contains 12 protons and 16 neutrons. What are the atoms?

A) chromium atoms B) two different elements C) two isotopes of an element D) negatively charged2. What are the majority of the elements on the

periodic table called? A) metals B) metalloids C) nonmetals D) compounds

3. Which element is a metalloid? A) bromine B) silicon C) potassium D) iron

Problem:4. An atom contains seven electrons and seven

protons. What element is this atom? Explain your answer.

Nitrogen, because the nitrogen atom has 7 protons.5. Cobalt-60 and cobalt-59 are isotopes. How can they

be the same element but have different mass numbers?

Different neutron number.

• Homework:

• Page 5, 6 (section 2)

• Page 12

• Remember elements 1-20 name, symbol, atomic number

quiz tomorrow! If you fail, retake the test!