classification of matter elements, compounds, mixtures
TRANSCRIPT
Classification of Matter
Elements, Compounds, Mixtures
Lesson Objective• Physical and Chemical Changes.• Elements• Compounds• Mixtures
Physical and Chemical Changes
• All reaction in Chemistry can be divided into two types of changes: Physical or Chemical.
• Physical Change:
• NO new substance is formed.• These changes are easily reversible or
temporary.• An example is dissolving salt in water.• Other examples of physical change include:
melting, boiling, mixing 2 solids or liquids.
• Chemical Change:
• A NEW substance is formed.• These changes are irreversible or permanent.• The new substance formed will have different
properties compared to its original elements. (E.g. different melting and different chemical reactions from the original substance.)
Physical and Chemical Changes
• One can recognize a chemical change from 2 observations:
• The new substance has a different appearance, such as different color or different physical state.
• An example is the electrolysis of water.• Reason: Electrolysis of water produces two new
substances, Hydrogen gas and oxygen gas. Hydrogen and oxygen are both gases but water is a liquid.
• A lot of heat is given out in a chemical changes.• Chemical changes are called chemical reactions.
Physical and Chemical Changes
Illustration of chemical changes
An Overview
Elements, Compounds and Mixtures
“ single, attached, play play…”
Introducing Little Miss “Element”
Hi! I am Little Miss “Element”I am PURE SUBSTANCE
I cannot be broken down into any simpler substance by
means of a chemical reaction* or electricity**!
*Chemical process refers to chemical reaction or heat
**Electricity refers to electrolysis
ElementsDefinition of an element:
An element is a pure substance which cannot be split up into two or more
simpler substances by chemical means.
Sugar is not an element as it can be broken down into carbon and water.
Note that an element:
• Consists of only one kind of atom,
• Cannot be broken down into a simpler type of matter by either physical or chemical means
• Can exist as either atoms (e.g. argon) or molecules (e.g., nitrogen).
Elements
Examples of elementsElements are made up of tiny particles
Elements can be further classified into two groups:
Is the smallest particle of an element and has
the same chemical propertiesof the element
Is made up of two or moreatoms that are chemically
bonded together
(note: these atoms are of the SAME element!!)
Hi, I am from the “Noble gas” family and I work alone
We same
same!!
These are elements!
Atoms of same element
Cu
copper element
Na
sodium element
He
helium element
Molecules of same element
HHydrogen gas element
O
H
OO
ozone
AtomsAn element is made of tiny particles called atoms.
The atoms of an element is different from that of another element.
Elements- Atoms
Microscopic view of the atoms of the element argon (gas phase).
Consists of only one kind
of atom
What is an atom?Examples of models of atoms:
H Na Cl
Hydrogen atom
Sodium atom
Chlorine atom
MoleculesVery few elements exists as
atoms besides elements such
as helium and neon.
Most elements exist as
molecules.
For example, hydrogen
is H2.
Ozone is O3.
Hydrogen (H2) is a
diatomic molecule.
Ozone (O3) is a
triatomic molecule.
Molecules consisting of a
few atoms are called
polyatomic molecules.
Elements-Molecules
Microscopic view of the molecules of the element nitrogen (gas phase).
Consists of only one kind
of atom
Examples of molecules (elements)
H H
N N
O
O
O
O O S
SS
SS
S
SS
Allotropes of Carbon molecule (element)
• Carbon is an element but made up of a very large molecule (also known as MACROMOLECULE)
• There are 3 types of carbon molecular structures– C60
– Diamond– Graphite
Chemical Symbols of Elements
Chemists use symbols to represent elements.
For example, O represents oxygen while Fe represents iron.
Element Symbol Element Symbol
Calcium Ca Mercury Hg
Carbon C Neon Ne
Hydrogen H Silicon Si
Iron Fe Sodium Na
Classification of Elements – Metals and Non-metals
There are two major groups of elements – metals and non-metals.
Iron is a metal. Oxygen is a non-metal.
There are some elements called metalloids which behave like both metals and non-metals.
Metals and non-metals are grouped separately on the Periodic Table.
What is an element?An element is a substance that cannot be broken down into two or more simpler substances by any chemical means.
- They are arranged in the Periodic Table, classified as metals and non-metals.- They may consist of atoms of same element or molecules of the same element. Metals (excluding hydrogen)
Non-metals (including hydrogen)
Physical Properties metals and non-metals
Metals Non-metals
Shiny appearance Dull appearance
Solids at r.t.p (except mercury)
Gases, liquids or solids at r.t.p (room temp & pressure)
Malleable, Ductile, Sonorous Brittle if solid (general)
High melting and boiling points
Low melting and boiling points
Good conductors of heat Poor conductors of heat
Good conductors of electricity
Poor conductors of electricity
(expect carbon and graphite)
Summarising
Elements
MetalsNon
Metals
Atoms Atoms Molecules
Introducing Little Miss “Compounds”
Harlow! Hehee!!!*giggles*
I am also a PURE SUBSTANCEI am made up of a fixed number
of two or more elements chemically combined.
CompoundsNote that a compound:
• can be broken down into a simpler type of matter (elements) by chemical means (but not by physical means),
• has properties that are different from its component elements, and
• always contains the same ratio of its component atoms.
A compound is a substance which is made up of two or more elements chemically combined together.
What is a compound?
- Chemical reactions taking place.
Qn: Is this a compound?
It only contains one type of element.
Qn: Is this a compound?
It only contains one type of element.
H
O
HO
O
Qn: Is this a compound?
It is not chemically combined.
So, what is a compound then?
H
Water Ammonia gas
Consists of two or more elements
And
They are chemically combined together!
Compounds
Microscopic view of the molecules of the compound water (gas phase). Oxygen atoms are red and hydrogen atoms are white.
ELEMENTSCOMPOUNDhydrogen
(colourless gas)
oxygen(colourless
gas)
lighted splint
heat, light and
explosion
water(colourless
liquid)
Making compounds from their elementsExample: Making water (picture)
Water molecule
Oxygen molecule
Hydrogen molecule
mixture of
hydrogen and
oxygen
water
Example: Making water (models)
heat, light and
explosion
Making compounds from their elements
Example: Making iron sulphide compound
Iron + sulphur iron sulphide
elementscompound
+
yellow grey
heat
heat
black
Little Miss “Compound” Property #1
I can be represented as a “chemical
formula”
The different elements present in
a compound are combined in a fixed
ratio
General Rules:- Only write the name of the metallic element first
- Write the number of atoms of any element in the compound in subscript (applies to only 2 or more atoms)
- “ide” will always be written at the end of the non metal element
Special Rules:• Does not apply to organic compounds
(chapter 18 onwards)
Little Miss “Compound” Property #2
I am formed by atoms of different elements.
However, I do not have the properties
as them.
Examples
• Na + Cl2 NaCl (s) (g) (s)
• H2 + O2 H2O (g) (g) (l)
Little Miss “Compound” Property #3
Because of my chemical bonds, I cannot be broken down by
physical means. I can only be broken down by chemical
reaction or electricity.
Electrolysis (breaking down of compound by electricity)
2MgCl(s) Mg(s) +Cl2(g)
Thermal Decomposition(breaking down of compound by heat)
HgO(s) Hg(s) + O2(g)
How do we name compounds? Rule 1
A compound made up of two elements has a name that ends in -ide.
• Sodium chloride — made up of the elements sodium and chlorine • Zinc oxide — made up of the elements zinc and oxygen • Carbon dioxide — made up of the elements carbon and oxygen
How do we name compounds? Rule 2
A compound that contains hydroxide ions , OH–
(a negatively charged ion made up of oxygen
and hydrogen) is named a hydroxide.
• Potassium hydroxide — contains potassium ions and hydroxide ions
How do we name compounds? Rule 3
A compound that contains a negatively
charged polyatomic ion containing oxygen
usually has a name ending in –ate.
• Copper(II) sulphate — contains oxygen atoms in the sulphate ion
• Sodium nitrate — contains oxygen atoms in the nitrate ion
Fixed Composition of Compounds
For example, water (H2O) is a compound made
only by joining together two atoms of hydrogen
to one atom of oxygen.
That is, the ratio of hydrogen atoms to oxygen
atoms in water is always 2 : 1.
A compound is made up of different elements
chemically combined in a fixed ratio.
Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.
Chemical Formula of a Compound
A compound can be represented by a chemical formula.
The chemical formula states • the types of atoms (i.e. elements) in the compound, • the ratio of the different atoms in the compound.
Types of atoms: hydrogen, oxygen
Ratio of H to O = 2:1
How do we write chemical formula?Rule 1
For many compounds that contain both metallic and non-metallic elements, the symbol of the metallic element is written first.
• calcium oxide (CaO) • sodium chloride (NaCl) • magnesium carbonate (MgCO3)
How do we write chemical formula?Rule 2
The number of atoms is written as a subscript, to the right of the atom’s symbol.
• water (H2O, not H2O or 2HO)
• magnesium carbonate (MgCO3, not MgCO3 or MgC3O)
How do we write chemical formula?Rule 3
It is not necessary to write the subscript ‘1’.
• water (H2O, not H2O1) • calcium oxide (CaO, not Ca1O1)
How do we write chemical formula?Rule 4
The oxygen atom is usually written at the end of the formula.
• water (H2O, not OH2) • carbon dioxide (CO2, not O2C) • nitric acid (HNO3, not O3NH)
How do we calculate the number of atoms in a formula?
Pb(NO3)2
Number of nitrogen (N) atoms
= 1 x 2 = 2
Number of lead (Pb) atoms =
1
Number of oxygen (O) atoms
= 3 x 2 = 6
Heat can be used to break down compounds into elements or simpler compounds. Such a chemical reaction is called thermal decomposition.
Compounds can be Decomposed
Mercury(II) oxide
Oxygen
Summarizing• A compound is made up of two or more
elements chemically joined together• A compound has a fixed composition• Every compound has a unique chemical
formula• A compound has a completely different
properties from its elements• A chemical reaction (decomposition or
electrolysis) is needed to separate the elements in the compound
Molecules- Elements or compounds?
• A molecule consists of two or more atoms of the same element, or different elements, that are chemically bound together.
• It can be a molecule of an element
• E.g. N2, O2, S8
• It can be molecule of a compound.
• H2O, CO2, NH3
N N O OS
SSS
S
S
SS
OH H
O OC N
H
HH
Think about this…ROJAK!!
Introducing Little Mr. “Mixture”
Burp!!!! I am messy!
I am formed when two or more substances joined together physically (without chemical
bonds)
I have the same properties as all the substances
AIR
I am his best friend!
MixturesDefinition of a mixture:
A mixture is not a pure substance as it contains a mixture of atoms of
molecules which are not chemically combined together.
Mixtures• Note that a mixture: • consists of two or more different elements
and/or compounds NOT chemically combined.• Can be homogeneous or non-homogeneous • can be separated into its components by
physical means, and • often retains many of the properties of its
components.
Microscopic view of a gaseous mixture containing two elements (argon and nitrogen) and a compound (water).
Mixtures
Mixtures
• Examples of mixtures include muddy water and air.
Air is made up of gases such as nitrogen and oxygen mixed together.
Little Mr “Mixture”I do not have a fixed composition of the substances.
A Mixture can be:• element + element
• element + compound• compound + compound
(Refer to page 59, Fig 4.7)
He is a “boo-boo!”
He can be separated to its substances by physical
methods
A mixture of 2 elements
A mixture of two elements, e.g. neon (Ne) and hydrogen (H2)
A mixture of 1 element and
1 compoundA mixture of one element and one compound, e.g. hydrogen (H2) and ammonia (NH3)
A mixture of 2 compounds
A mixture of two compounds, e.g. water vapour (H2O) and carbon dioxide (CO2)
Mr Alloy
Alloy: What is it??• It is a mixture of metals with
other elements
• Alloy metals are generally stronger and better in physical properties
• Examples– Steel (Iron + Carbon)– Stainless Steel (Nickel + Iron +
Chromium + carbon)– Brass (Copper + Zinc)
Yup!That’s
ME!
Can you differentiate?
Compound Mixture of element & compound
Mixture of 2 elements-Alloy
Molecules of an element
Mixture of 2 elements
ConclusionAn element is a pure substance which cannot be
split up into two or more simpler substances by chemical means.
A compound consist of a fixed number of different kinds of atoms chemically combined together.
A mixture is not a pure substance as it contains a mixture of atoms of molecules which are not chemically combined together.
Difference between mixtures and compounds.
Compounds
E.g.
Water H2O
Mixtures
E.g.
Salt solution
Separation Cannot be separated into its constituents by physical methods. Separation can only be done by chemical methods or by electricity.
e.g. Water can only be separated into Hydrogen and Oxygen by Electrolysis.
Can be easily separated into its constituents by physical
methods.
e.g. Salt can be obtained from its solution by
evaporation. Water can be obtained by simple
distillation.
Difference between mixtures and compounds.Compounds
E.g.
Water H2O
Mixtures
E.g.
Salt solution
Composition The composition is fixed. The constituents (elements) in the compound are combined in definite amount.
e.g. To form one molecule of water, two atoms of Hydrogen and one atom of Oxygen is needed.
Has no fixed composition. The amount of constituents in a mixture can vary.
e.g. The amount of salt added into the water to make salt solution can vary and vice versa.
Difference between mixtures and compounds.Compounds
E.g.
Water H2O
Mixtures
E.g.
Salt solution
Properties The physical and chemical properties of the compound is different from the properties of its constituents.
e.g. Hydrogen and Oxygen are gases while water is a liquid at room temperature and pressure.
e.g. Water has a fixed melting and boiling point.
The mixture does not have its own properties. It has the average physical and chemical properties of the constituents that made it up. (Each constituents still retain its own properties)
e.g. The salt solution still retains its salt taste.
e.g. Salt solution does not have a fixed melting or boiling point, but
rather over a range of temperature.
Difference between mixtures and compounds.
Compounds
E.g.
Water H2O
Mixtures
E.g.
Salt solution
Energy Change
Energy is usually given out or occasionally taken in when a compound is formed.
Normally little or no energy is given out or
taken in when a mixture is formed.
Differences between mixtures and compounds
*giggles*
HeE stupid…
Laugh what? I know I am a
little “bushy and hairy” than
you…
Little Miss CompoundMr Messy
Comparison between mixtures and compounds
FixedVariableMp / Bp
Has a fixed compositionDoes not have a fixed composition
Composition
A chemical reaction takes place when a compound
is formed
No chemical change takes place when a mixture in formed
Energy Change
Properties are unique and different from its elements
Same properties as its components
Properties
(chemical / physical)
Elements in a compound Cannot be separated by
physical methods
Components can be separated by physical
methods
Separation
/breakdown
CompoundMixture
Challenge Time • Is mineral water an element, mixture or
compound?
Challenge Time
• Are YOU an element, mixture or compound?
EXTRA!• Human body is made up of 28 elements?• About 99% our mass is made up of the 6
main elements– Oxygen (65%)– Carbon (18%)– Hydrogen (10%)– Nitrogen (3%)– Calcium (1.5%)– Phosphorus (1.5%)
The End……