Learning Objective

In this lesson we will revise the classification of matter and atomic structure.

Learning Outcomes

By the end of this lesson you will be able to:

  • Distinguish between pure substances and mixtures.
  • Distinguish between elements and compounds.
  • Describe the arrangement of atoms in pure substances.
  • Describe the subatomic structure of atoms, including protons, neutrons and electrons.
  • Define atomic number and mass number, and explain what isotopes are.
  • Describe the configuration of electrons for the first 20 elements.

Atoms, Elements and Compounds

1 | Pure Substances and Mixtures

2 | Elements and Compounds

3 | Atoms, Molecules and Lattices

4 | Structure of Atoms

5 | Electron Configuration

6 | Summary

 

 atoms elements and compounds worksheet  year 10 chemistry pdf workbook  Year 10 Chemistry Print Workbook Australian Curriculum

Click images to preview the worksheet for this lesson and the Year 10 Chemistry Workbook (PDF and print versions)

 


Pure Substances and Mixtures

  • Chemistry is the study of the physical and chemical properties of matter.
  • Matter can be divided into pure substances and mixtures.
  • Pure substances have fixed physical and chemical properties, such as melting and boiling point, and chemical reactivity.

 
gold pure substance element

Gold is a pure substance – it has fixed physical and chemical properties.

(Image: James St. John, Wikimedia Commons)

 

  • Mixtures have variable physical and chemical properties.
  • They are physical combinations of two or more pure substances, which can be physically separated.

 
mud mixture

Mud is a mixture – it has variable physical and chemical properties.

(Image: Hans, Pixabay)

 


Elements and Compounds

  • Pure substances include elements and compounds.
  • Elements cannot be broken down into simpler substances.
  • Examples of elements include chlorine, sulfur and copper.

 

 chlorine gas pure element  chlorine gas pure element  copper pure element

Chlorine, sulfur and copper are elements – they have fixed physical and chemical properties, and cannot be broken down into simpler substances.

(Images: W. Oelen, Wikimedia Commons; Ben Mills, Wikimedia Commons; Jonathan Zander, Wikimedia Commons)

 

  • Compounds can be broken down (chemically) into simpler substances.
  • Examples of compounds include water, methane and copper sulfate.

 

Copper sulfate is a compound – it has fixed physical and chemical properties, but can be broken down into simpler substances (the elements copper, sulfur and oxygen).

(Image: Stephanb, Wikimedia Commons)

 


Chemical Subunits: Atoms, Molecules and Lattices

  • A chemical subunit can be defined as the smallest building block of a pure substance that is unique to that substance.
  • Atoms are the simplest type of chemical subunit, forming the building blocks of all matter.
  • Atoms can exist individually, but more often they are connected to other atoms by chemical bonds, forming molecules or lattices.
  • Molecules are discrete arrangements of atoms joined by chemical bonds.

 
molecules structure atom arrangement

Molecules are discrete structures held together by chemical bonds.

 

  • Lattices are networks of atoms joined by chemical bonds.

 
lattice structure atom arrangement

Lattices are continuous structures held together by chemical bonds.

 

  • Molecules and lattices may be composed of the same type of atom, or they may be composed of two or more different types of atoms, in fixed arrangements.

 

Arrangement of Atoms in Pure Substances

  • Pure substances have fixed properties because they are made up of one type of chemical subunit.
  • Mixtures have variable properties because they are made up of more than one type of chemical subunit.

 

Arrangement of Atoms in Elements

  • Elements are pure substances that cannot be broken down into simpler substances because their subunits consist of one type of atom.
  • These atoms may exist individually, or as molecules or lattices.
  • Examples
  • The atoms in helium exist individually.
  • The atoms in oxygen exist as molecules containing pairs of oxygen atoms.
  • The atoms in carbon (diamond) exist as a continuous network.

 

 helium atoms arrangement  oxygen molecules atom arrangement  carbon lattice atom arrangement

Atoms in elements can exist individually, as molecules or as lattices.

 

Arrangement of Atoms in Compounds

  • Compounds are pure substances that can be broken down into simpler substances because their subunits consist of more than one type of atom.
  • These atoms may exist as molecules or lattices.
  • Examples
  • The atoms in carbon dioxide exist as molecules containing one carbon atom and two oxygen atoms.
  • The atoms in silicon dioxide (quartz) exist as continuous networks of silicon and oxygen atoms, in a 1:2 ratio.

 

 carbon dioxide molecules atom arrangement  silicon dioxide lattice atom arrangement

Atoms in compounds can exist as molecules or as lattices.

 


Structure of Atoms

  • Atoms are made up of three main subatomic particlesprotons, neutrons and electrons.
  • Protons and neutrons form a cluster at the centre of the atom, called the nucleus.
  • Electrons orbit the nucleus in electron shells, forming an electron cloud.

 
structure of atom

Atoms are made up of protons, neutrons and electrons.

 

Protons

  • Protons are subatomic particles with a positive charge (+1).
  • Protons have a mass of 1 atomic mass unit.
  • The number of protons in an atom determines the type of atom.
  • Examples
  • If an atom has 2 protons, it is a helium atom.
  • If an atom has 6 protons, it is a carbon atom.
  • If an atom has 26 protons, it is an iron atom.
  • The number of protons in an atom is known as the atomic number.

atomic proton number

 

Neutrons

  • Neutrons are subatomic particles with no charge.
  • Neutrons have a mass of 1 atomic mass unit.
  • The number of neutrons in a particular type of atom can vary.
  • For example, 99% of carbon atoms have 6 neutrons, while 1% have 7 neutrons.
  • The total number of protons and neutrons in an atom is known as the mass number.

mass number protons neutrons

  • Atoms that have the same number of protons but a different number of neutrons are called isotopes.
  • Therefore, isotopes of an element have the same atomic number, but different mass numbers.

 
isotope carbon-12 carbon-13

Carbon-12 and carbon-13 are isotopes of carbon.

 

Electrons

  • Electrons are subatomic particles with a negative charge (–1).
  • Electrons have a mass of 1/1840 of an atomic mass unit.
  • Therefore, almost all of the mass of an atom is in the nucleus.
  • The number of electrons in an atom equals the number of protons.
  • Therefore, atoms have no overall charge.

number of electrons equals number of protons

 


Electron Configuration

  • The arrangement of electrons in shells around the nucleus of an atom is referred to as the electron configuration.
  • Electron shells fill up from the inner shell first.
  • The further away from the nucleus a shell is, the larger it is and the more electrons it can hold.
  • The first shell (closest to the nucleus) can hold a maximum of 2 electrons.
  • The second shell can hold a maximum of 8 electrons.
  • The third shell can hold a maximum of 18 electrons, but once it has 8 electrons, the fourth shell begins to fill.
  • For example, even though shell 3 can hold a maximum of 18 electrons, potassium has 8 electrons in the third shell and 1 electron in the fourth shell.
  • The maximum number of electrons that can exist in a shell is summarised by the following formula, where n is the shell number (energy level).

maximum electrons shell filling formula

 

Shorthand Electron Configuration

  • The electron configuration of an element can be written in an abbreviated form, showing the numbers of electrons in each shell.
  • Example
  • A silicon atom has 14 electrons. There are two electrons in the first shell, eight electrons in the second shell and four electrons in the third shell. The electron configuration of silicon can therefore can be written as 2,8,4.

 
simple electron configuration silicon

Silicon has the electron configuration 2,8,4.

 

Valence Electrons

  • The outermost electron shell is known as the valence shell.
  • It can hold a maximum of 8 electrons, regardless of which shell number it is; the only exception is when the valence shell is the only shell – in this case, the maximum number of electrons is 2.
  • Electrons in the valence shell are known as valence electrons.
  • In the example above, silicon has four valence electrons.
  • The number of valence electrons in an atom largely determines the chemical properties of an element.

 
valence electron shell

Valence electrons determine an element’s chemical stability.

 


Summary

  • A chemical subunit is the smallest building block of a pure substance that is unique to that substance.
  • Atoms are the simplest type of chemical subunit.
  • Atoms can exist individually or connected to other atoms by chemical bonds.
  • Molecules are discrete arrangements of atoms joined by chemical bonds.
  • Lattices are networks of atoms joined by chemical bonds.
  • Pure substances are made up of one type of chemical subunit.
  • They have defined physical and chemical properties.
  • Elements are pure substances made up of one type of atom.
  • These atoms may exist individually, or as molecules or lattices.
  • Elements cannot be broken down into simpler substances.
  • Compounds are pure substances made up of two or more different types of atoms.
  • These structures may be molecules or lattices.
  • Compounds can be broken down (chemically) into simpler substances.
  • Atoms are made up of three main subatomic particles – protons, neutrons and electrons.
  • Protons and neutrons form a cluster at the centre of the atom, called the nucleus.
  • Electrons orbit the nucleus, in electron shells, forming an electron cloud.
  • Protons have a mass of 1 atomic mass unit and a positive charge (+1).
  • Neutrons have a mass of 1 atomic mass unit and no charge.
  • Electrons have a mass of 1/1840 of an atomic mass unit and a negative charge (–1).
  • Atoms that have the same number of protons but a different number of neutrons are called isotopes.
  • The atomic number of an atom is equal to the number of protons in the atom.
  • It determines the type of atom.
  • The mass number of an atom is equal to the total number of protons and neutrons in the atom.
  • This is the number of particles in the nucleus, which largely determines the mass of an atom.
  • Electron configuration describes the arrangement of electrons in shells around the nucleus of an atom.
  • A maximum of 2 electrons can occupy the first shell.
  • A maximum of 8 electrons can occupy the second shell.
  • A maximum of 18 electrons can occupy the third shell, but the fourth shell will begin to fill once the third shell contains 8 electrons.
  • A maximum of 8 electrons can occupy the valence shell (outermost shell).

 
molecules

(Image: MasterTux, Pixabay)

(Header image: geralt, Pixabay)

 

 atoms elements and compounds worksheet  year 10 chemistry pdf workbook  Year 10 Chemistry Print Workbook Australian Curriculum

Click images to preview the worksheet for this lesson and the Year 10 Chemistry Workbook (PDF and print versions)