An element is a pure substance made of atoms that all contain the same number of protons and cannot be broken down into anything simpler by chemical means. There are around 118 elements listed in the Periodic Table.

A compound is a pure substance made up of two or more elements chemically combined. Compounds cannot be separated into their elements by physical means and there is an unlimited number of possible compounds.

True or False? A mixture can be separated into its components by physical methods.

True. A mixture contains two or more substances that are not chemically combined, so they retain their individual properties and can be separated by physical methods such as filtration or evaporation.

Carbon dioxide (CO 2 ) is a .......... because it contains two different .......... that are .......... combined together.

Carbon dioxide (CO 2 ) is a compound because it contains two different elements that are chemically combined together.

What is the key difference between a compound and a mixture ?

In a compound , elements are chemically bonded together and cannot be separated by physical means. In a mixture , substances are not chemically combined and can be separated by physical methods such as filtration. Compounds have fixed compositions; mixtures do not.

Give two examples of a mixture and explain why each one qualifies.

Sand and water is a mixture because the sand and water are not chemically combined and can be separated by filtration. Sulfur powder and iron filings is a mixture because the two substances retain their individual properties and can be separated by using a magnet.

True or False? Elements can be broken down into simpler substances by chemical reactions.

False. Elements cannot be split into anything simpler by chemical means. They are the simplest type of pure substance, made of atoms all with the same number of protons.

A .......... is a combination of two or more substances that are .......... chemically combined and can be separated by .......... methods.

A mixture is a combination of two or more substances that are not chemically combined and can be separated by physical methods.

How many elements are there in copper(II) sulfate (CuSO 4 ) and does that make it an element, compound or mixture?

Copper(II) sulfate (CuSO 4 ) contains three elements — copper, sulfur and oxygen — which are chemically combined. This makes it a compound , not a mixture or an element.

What is the nucleus of an atom?

The nucleus is the central region of an atom containing protons and neutrons . It carries almost all of the atom's mass. Electrons move rapidly around the nucleus in shells.

What are the relative mass and relative charge of a proton , a neutron and an electron ?

A proton has relative mass 1 and charge 1+. A neutron has relative mass 1 and charge 0. An electron has negligible mass (approximately 1/1840) and charge 1-.

True or False? The mass of an atom is concentrated mainly in its electron shells.

False. Almost all of the mass of an atom is contained in the nucleus , where the protons and neutrons are located. Electrons have negligible mass and contribute virtually nothing to the overall mass.

What is the proton number (atomic number)?

The proton number (or atomic number, symbol Z ) is the number of protons in the nucleus of an atom. It is also equal to the number of electrons in a neutral atom and determines the element's position on the Periodic Table.

The mass number (nucleon number) is the total number of .......... and .......... in the nucleus. The number of neutrons equals the mass number .......... the proton number.

The mass number (nucleon number) is the total number of protons and neutrons in the nucleus. The number of neutrons equals the mass number minus the proton number.

An atom has atomic number 29 and mass number 63. How many protons, electrons and neutrons does it contain?

Protons = 29 (equal to the atomic number). Electrons = 29 (neutral atom has equal protons and electrons). Neutrons = 63 − 29 = 34.

True or False? All atoms of the same element have the same number of protons.

True. The number of protons defines which element an atom is. All atoms of the same element always have the same proton number (atomic number), regardless of the number of neutrons.

In a neutral atom, the number of .......... is always equal to the number of .......... .

In a neutral atom, the number of protons is always equal to the number of electrons .

Why is the mass of an electron described as negligible when calculating the mass of an atom?

An electron has a relative mass of approximately 1/1840, which is tiny compared with the relative mass of 1 for each proton and neutron. Because electrons contribute so little to the total, their mass is considered negligible and the mass of the atom is taken as the number of protons plus neutrons .

What is relative atomic mass ( A r )?

Relative atomic mass ( A r ) is the average mass of one atom of an element compared with 1/12th the mass of a carbon-12 atom. Because it is a ratio, A r has no units .

What is electronic configuration ?

Electronic configuration is the notation that shows how electrons are distributed across the shells (energy levels) of an atom. It is written as numbers separated by commas, e.g. 2,8,1 for sodium.

How many electrons can fit in the first, second and third electron shells?

The first shell can hold a maximum of 2 electrons, the second shell can hold 8 electrons, and the third shell can hold 8 electrons (in the simplified model used at this level).

Magnesium has 12 electrons. Its electronic configuration is .......... because it has .......... electrons in the first shell, .......... in the second and .......... in the third.

Magnesium has 12 electrons. Its electronic configuration is 2,8,2 because it has 2 electrons in the first shell, 8 in the second and 2 in the third.

True or False? All elements in the same group of the Periodic Table have the same number of electrons in their outer shell.

True. Elements in the same group share the same number of outer-shell electrons. This is why elements in the same group have similar chemical properties, as chemical reactivity is determined by the outer electrons.

How does the electronic configuration of an element indicate which period and group it belongs to?

The number of occupied shells gives the period number. The number of electrons in the outermost shell gives the group number (for Groups I to VII). For example, chlorine (2,8,7) has 3 shells so is in Period 3 and 7 outer electrons so is in Group VII.

Noble gases are unreactive because they have a .......... outer shell of electrons, making them very .......... .

Noble gases are unreactive because they have a full outer shell of electrons, making them very stable .

True or False? Electrons fill the outermost shell first before filling shells closer to the nucleus.

False. Electrons fill the shell closest to the nucleus first. Only once a shell is full do additional electrons move to the next shell further out.

Write the electronic configuration of a sodium ion Na + and explain why it differs from the sodium atom.

A sodium atom has 11 electrons with configuration 2,8,1. A sodium ion (Na + ) has lost one electron, leaving 10 electrons, giving the configuration 2,8 . This is the same as the noble gas neon, giving Na + a stable full outer shell.

What is the valence shell and why is it chemically important?

The valence shell is the outermost occupied electron shell of an atom. It is chemically important because atoms react with other atoms to fill or empty this shell, achieving a more stable full outer-shell configuration like the noble gases.

IGCSEScienceCambridge (CIE)Combined ScienceChemistryFlashcards2. Atoms, Elements & CompoundsAtomic Structure & the Periodic Table

Atomic Structure & the Periodic Table (Cambridge (CIE) IGCSE Combined Science: Chemistry): Flashcards

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Cards in this collection (28)

What is an element?
An element is a pure substance made of atoms that all contain the same number of protons and cannot be broken down into anything simpler by chemical means. There are around 118 elements listed in the Periodic Table.
What is a compound?
A compound is a pure substance made up of two or more elements chemically combined. Compounds cannot be separated into their elements by physical means and there is an unlimited number of possible compounds.
True or False?
A mixture can be separated into its components by physical methods.
True.
A mixture contains two or more substances that are not chemically combined, so they retain their individual properties and can be separated by physical methods such as filtration or evaporation.
Carbon dioxide (CO₂) is a .......... because it contains two different .......... that are .......... combined together.
Carbon dioxide (CO₂) is a compound because it contains two different elements that are chemically combined together.
What is the key difference between a compound and a mixture?
In a compound, elements are chemically bonded together and cannot be separated by physical means. In a mixture, substances are not chemically combined and can be separated by physical methods such as filtration. Compounds have fixed compositions; mixtures do not.
Give two examples of a mixture and explain why each one qualifies.
Sand and water is a mixture because the sand and water are not chemically combined and can be separated by filtration. Sulfur powder and iron filings is a mixture because the two substances retain their individual properties and can be separated by using a magnet.
True or False?
Elements can be broken down into simpler substances by chemical reactions.
False.
Elements cannot be split into anything simpler by chemical means. They are the simplest type of pure substance, made of atoms all with the same number of protons.
A .......... is a combination of two or more substances that are .......... chemically combined and can be separated by .......... methods.
A mixture is a combination of two or more substances that are not chemically combined and can be separated by physical methods.
How many elements are there in copper(II) sulfate (CuSO₄) and does that make it an element, compound or mixture?
Copper(II) sulfate (CuSO₄) contains three elements — copper, sulfur and oxygen — which are chemically combined. This makes it a compound, not a mixture or an element.
What is the nucleus of an atom?
The nucleus is the central region of an atom containing protons and neutrons. It carries almost all of the atom's mass. Electrons move rapidly around the nucleus in shells.
What are the relative mass and relative charge of a proton, a neutron and an electron?
A proton has relative mass 1 and charge 1+. A neutron has relative mass 1 and charge 0. An electron has negligible mass (approximately 1/1840) and charge 1-.
True or False?
The mass of an atom is concentrated mainly in its electron shells.
False.
Almost all of the mass of an atom is contained in the nucleus, where the protons and neutrons are located. Electrons have negligible mass and contribute virtually nothing to the overall mass.
What is the proton number (atomic number)?
The proton number (or atomic number, symbol Z) is the number of protons in the nucleus of an atom. It is also equal to the number of electrons in a neutral atom and determines the element's position on the Periodic Table.
The mass number (nucleon number) is the total number of .......... and .......... in the nucleus. The number of neutrons equals the mass number .......... the proton number.
The mass number (nucleon number) is the total number of protons and neutrons in the nucleus. The number of neutrons equals the mass number minus the proton number.
An atom has atomic number 29 and mass number 63. How many protons, electrons and neutrons does it contain?
Protons = 29 (equal to the atomic number). Electrons = 29 (neutral atom has equal protons and electrons). Neutrons = 63 − 29 = 34.
True or False?
All atoms of the same element have the same number of protons.
True.
The number of protons defines which element an atom is. All atoms of the same element always have the same proton number (atomic number), regardless of the number of neutrons.
In a neutral atom, the number of .......... is always equal to the number of .......... .
In a neutral atom, the number of protons is always equal to the number of electrons.
Why is the mass of an electron described as negligible when calculating the mass of an atom?
An electron has a relative mass of approximately 1/1840, which is tiny compared with the relative mass of 1 for each proton and neutron. Because electrons contribute so little to the total, their mass is considered negligible and the mass of the atom is taken as the number of protons plus neutrons.
What is relative atomic mass (A_r)?
Relative atomic mass (A_r) is the average mass of one atom of an element compared with 1/12th the mass of a carbon-12 atom. Because it is a ratio, A_r has no units.
What is electronic configuration?
Electronic configuration is the notation that shows how electrons are distributed across the shells (energy levels) of an atom. It is written as numbers separated by commas, e.g. 2,8,1 for sodium.
How many electrons can fit in the first, second and third electron shells?
The first shell can hold a maximum of 2 electrons, the second shell can hold 8 electrons, and the third shell can hold 8 electrons (in the simplified model used at this level).
Magnesium has 12 electrons. Its electronic configuration is .......... because it has .......... electrons in the first shell, .......... in the second and .......... in the third.
Magnesium has 12 electrons. Its electronic configuration is 2,8,2 because it has 2 electrons in the first shell, 8 in the second and 2 in the third.
True or False?
All elements in the same group of the Periodic Table have the same number of electrons in their outer shell.
True.
Elements in the same group share the same number of outer-shell electrons. This is why elements in the same group have similar chemical properties, as chemical reactivity is determined by the outer electrons.
How does the electronic configuration of an element indicate which period and group it belongs to?
The number of occupied shells gives the period number. The number of electrons in the outermost shell gives the group number (for Groups I to VII). For example, chlorine (2,8,7) has 3 shells so is in Period 3 and 7 outer electrons so is in Group VII.
Noble gases are unreactive because they have a .......... outer shell of electrons, making them very .......... .
Noble gases are unreactive because they have a full outer shell of electrons, making them very stable.
True or False?
Electrons fill the outermost shell first before filling shells closer to the nucleus.
False.
Electrons fill the shell closest to the nucleus first. Only once a shell is full do additional electrons move to the next shell further out.
Write the electronic configuration of a sodium ion Na⁺ and explain why it differs from the sodium atom.
A sodium atom has 11 electrons with configuration 2,8,1. A sodium ion (Na⁺) has lost one electron, leaving 10 electrons, giving the configuration 2,8. This is the same as the noble gas neon, giving Na⁺ a stable full outer shell.
What is the valence shell and why is it chemically important?
The valence shell is the outermost occupied electron shell of an atom. It is chemically important because atoms react with other atoms to fill or empty this shell, achieving a more stable full outer-shell configuration like the noble gases.

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