Key Concepts in Chemistry: SC3 + SC4 Flashcards
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
What is a group on the periodic table?
A vertical column of elements with the same number of outer shell electrons
What is a period on the periodic table?
A row of elements with the same number of electron shells
Define isotopes
Atoms of an element with the same number of protons and electrons but a varying number of neutrons
What is the standard isotope?
Carbon 12
What is the equation for the relative atomic mass?
((% of isotope 1 x mass of isotope 1) + (% of isotope 2 + mass of isotope 2))/ the number of atoms
Where is most of the mass of the atom concentrated in?
The nucleus of the atom
Why do atoms of different elements vary?
They have different amounts of protons in their nucleus, which changes their physical properties
Why isn’t the relative atomic mass of many elements a whole number?
It is the average of all the atoms in an element, which means that the average isn’t always a whole number
What are valence electrons?
Electrons on the outmost shell which are involved in reactions
What is the average atomic radius?
0.1 nm (1 x 10^-10 m)
What is the average atomic nucleus radius?
10,000 times smaller than an atom (1 x 10^-14 m)
Who discovered the ‘plum pudding’ model of the atom?
JJ Thompson
What is the plum pudding model of the atom?
Atoms are balls of positively charge with negative electrons embedded in it
What is the nuclear model of the atom?
Atoms are made of a small positive nucleus orbited by negative electrons.
What were the problems with the nuclear model of the atom?
Model claimed that electrons orbited the nucleus but didn’t explain why
What did JJ Thompson discover?
The electron
What were the problems with the plum pudding model?
Model didn’t have a nucleus
How did Bohr modify the Nuclear model?
- stated electrons moved around the nucleus in orbit of fixed sizes and energies
- the energies of the electron were quantized so they couldn’t occupy values of energy between fixed levels
What were the problems with Bohr’s modifications?
- They didn’t work with heavier atoms
- Moving electrons should emit energy and collapse into the nucleus
What is the quantum model of the atom?
- Schrödinger claimed that electrons don’t move in set paths, but waves
- he also said it was impossible to know the exact location of an electron at any given time
- instead suggested the ‘cloud of probability’ called orbitals in which we are likely to find an electron
Who discovered neutrons?
James Chadwick
