Key Concepts in Chemistry: SC3 + SC4
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Describe how Mendeleev arranged the elements in the periodic table.
• In order of increasing relative atomic mass. • Left gaps for undiscovered elements. • In matching physical and chemical properties.
Who made the periodic table?
Dmitri Mendeleev
Describe how Mendeleev used his table to predict the existence and properties of some elements not then discovered.
He left gaps for undiscovered elements.
Explain the meaning of atomic number of an element
The atomic number is the number of proton in the nucleus of an atom.
Describe the properties of metals
• Metals are malleable. • insoluble in water • high melting and boiling points • Good conductors of heat and electricity
Define electron configuration
The way in which an atom’s electrons are arranged in its shells
What also happens if the elements in the periodic table are arranged in increasing atomic number?
• Elements with similar properties are in the same column/ group • Non-metals are on the right of the table • metals are on the left side of the table
What is common about the electron shells for the first twenty elements?
• first shell can contain up to 2 electrons • second and third shell can contain up to 8 electrons
Explain why atoms contain equal numbers of protons and electrons
They have equal numbers of positive and negative charges, and so are neutral overall.
How is the electron configuration related to the position of an element on the periodic table?
• the number of shells there are in an electronic configuration of an element is represented in the periodic table as the period number that the element is situated in • The number of electrons in the outermost shell of an element is represented in the periodic table as the group number that the atom is in • the number of electrons in an atom is the same as its atomic number unless it is an ion • In the first twenty elements, the first and innermost shell will only have 2 electrons max
What did Dalton’s theory claim?
• All matter is made up of tiny particles called atoms • Atoms are tiny, hard spheres that are indivisible • atoms of different elements are different from each other • Compounds are combinations of different elements • atoms of an element are identical to each other • during chemical reactions, atoms rearrange to form different substances —> Therefore, they cannot be destroyed • all atoms in an element are identical
What is the relative charge of a proton?
+1
What is the relative charge of a neutron?
0
What is the relative charge of an electron?
-1
What is the mass of a proton?
1
What is the mass of a neutron?
1
What is the mass of an electron?
negligible/ 1/2000
How have Dalton’s ideas been disproven?
Subatomic particles mean that atoms are divisible
Describe the structure of an atom.
A nucleus containing protons and neutrons, surrounded by electrons in shells
What is the mass number of an atom?
The total amount of protons and neutrons in the nucleus.
Why doesn’t an atom have an overall charge?
Both the protons and electrons are of an equal number and so the charges cancel each other out
Who discovered the atom’s nucleus?
Ernest Rutherford
Describe Rutherford’s experiment which allowed him to discover the atom’s nucleus
• Fired alpha particles at a thin gold foil • expected that all of them would pass through • Some were deflected • those that were deflected were had said to hit the nucleus • but majority passed through indicating that atoms are mainly empty space
Define ‘atomic mass’
The average mass of all the isotopes in an element