2.2 Atomic Structure & the Periodic Table (Cambridge (CIE) O Level Chemistry): Flashcards
Exam code: 5070
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- FrontAtomic Structure
Define proton number (atomic number).
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Define proton number (atomic number).
The proton number (or atomic number) is the number of protons in the nucleus of an atom. In a neutral atom, it also equals the number of electrons.
What term describes the arrangement of electrons in the shells of an atom, written as a series of numbers separated by commas?
Electronic configuration. For example, the electronic configuration of carbon (proton number 6) is 2,4.
In an atom, protons and neutrons are found in the ______, while electrons move in ______ around it.
In an atom, protons and neutrons are found in the nucleus, while electrons move in shells around it.
Complete the table showing the maximum number of electrons each shell can hold.
Shell
Maximum electrons
1st
2nd
3rd
Shell
Maximum electrons
1st
2
2nd
8
3rd
8
A proton has a relative mass of ______ and a relative charge of ______.
A neutron has a relative mass of ______ and a relative charge of ______.
A proton has a relative mass of 1 and a relative charge of +1.
A neutron has a relative mass of 1 and a relative charge of 0 (neutral).
True or False?
An ion has the same electronic configuration as the neutral atom it formed from.
False.
An ion is formed by gaining or losing electrons from the outer shell. A Na+ ion has lost one electron, so its electronic configuration is 2,8, not the 2,8,1 of a neutral sodium atom.
True or False?
A neutral atom of chlorine (proton number 17, mass number 35) contains 18 neutrons.
True.
Number of neutrons = mass number − proton number = 35 − 17 = 18.
How does the electronic configuration of an element reveal its group and period in the Periodic Table?
The number of outer shell electrons equals the element's group number (for Groups I to VII).
The number of occupied shells equals the period number.
The mass number of an atom is the total number of ______ and ______ in the nucleus.
The mass number of an atom is the total number of protons and neutrons in the nucleus.
Elements in the same ______ of the Periodic Table have the same number of ______ shell electrons.
Elements in the same group of the Periodic Table have the same number of outer shell electrons.
Why does a negative ion have more electrons than protons?
A negative ion is formed when an atom gains electrons. The number of protons in the nucleus stays the same, but the extra electrons mean the ion has more electrons than protons, giving it an overall negative charge.
True or False?
A magnesium atom (proton number 12) has the electronic configuration 2,8,2.
True.
Magnesium has 12 electrons. The first shell holds 2, the second holds 8, and the remaining 2 occupy the third shell: 2,8,2.
True or False?
A sodium ion (Na+) has the same number of electrons as a sodium atom.
False.
A sodium atom has 11 electrons. A Na+ ion has lost one electron, so it has only 10 electrons.
What is the electronic configuration of a calcium ion (Ca2+)?
A calcium atom (proton number 20) has the configuration 2,8,8,2. When it forms a Ca2+ ion, it loses 2 electrons from its outer shell, giving the configuration 2,8,8.
True or False?
The electronic configuration of a chlorine atom (proton number 17) is 7,8,2.
False.
The correct electronic configuration of chlorine is 2,8,7.
Electrons fill shells from the innermost outwards: 2 in the first shell, 8 in the second, and 7 in the third.
A phosphorus atom (proton number 15) has the electronic configuration 2,8,______.
A phosphorus atom (proton number 15) has the electronic configuration 2,8,5.
This places it in Group V and Period 3 of the Periodic Table.
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