Topic 1: Atomic Structure and the Periodic Table Flashcards
Structure of the atom
The structure of an atom is made up of protons, neutrons and electrons
What is the relative mass and relative charge of a proton, neutron and electron ?
Protons: Have a relative charge of +1 and a relative mass of 1
Neutrons: Have a relative charge of 0 and a relative mass of 1
Electrons: Have a relative charge of -1 and a relative mass of 1/1840
What is meant by atomic number and mass number?
Atomic number: The number of protons in an atom’s nucleus.
Mass number: The total number of protons and neutrons in an atom’s nucleus.
How to determine the number of each type of sub-atomic particle in an atom?
Number of protons: The number of protons in an atom is equal to its atomic number.
Number of electrons: In a neutral atom, the number of electrons is equal to the number of protons.
Number of neutrons: The number of neutrons in an atom is equal to its mass number minus its atomic number.
What is an isotope?
An isotope is an atom of an element that has the same number of protons but a different number of neutrons
What is relative isotopic mass and relative atomic mass?
Relative isotopic mass is the mass of an isotope of an element compared to 1/12th of the mass of a carbon-12 atom.
Relative atomic mass is the average mass of an element’s atoms compared to one-twelfth the mass of a carbon-12 atom
What is relative molecular mass and relative formula mass?
Relative molecular mass is the average mass of a molecule compared to one-twelfth of the mass of a carbon-12 atom.
Relative formula mass is the sum of the relative atomic masses of all the atoms in a substance’s formula.
How to find relative molecular mass?
The sum of the relative atomic masses of all the atoms in a molecule. For example, to calculate the relative molecular mass of ethanol (C2H5OH), you can add up the relative atomic masses of each atom in the molecule: Mr(C2H5OH) = 46.0.
How to find relative formula mass?
To calculate the relative formula mass of a substance, you determine how many atoms of each element are in the chemical formula, find the relative atomic masses of each element on the periodic table and add together the atomic masses.
How do you analyse and interpret data from mass spectrometry?
We can determine the relative molecular mass by looking at the peak furthest to the right. The peaks to the left are peaks caused by fragments: For CO2, for example, the peak furthest to the right is due to the CO2 molecular ion. The peak at 28 is due to the CO molecular ion (an oxygen atom has been lost).
How do you predict mass spectra of chlorine?
You can predict how a mass spectrum might appear for a given compound.
A compound containing one chlorine atom will therefore have two molecular ion peaks due to the two different isotopes it can contain
35Cl = M+ peak
37Cl = [M+2] peak
How can mass spectrometry be used to determine relative molecular mass?
Mass spectrometry can be used to determine the relative molecular mass (RMM) of a compound by finding the peak with the highest mass to charge ratio (m/z) value on the mass spectrum.
Define first ionisation energy and successive ionisations energies
First ionization energy is the amount of energy needed to remove the outermost electron from a neutral atom of an element in a gaseous state.
Successive ionization energies are the energies required to remove electrons one by one from a mole of gaseous ions or atoms.
How are ionisation energies influenced by protons?
The more protons in the nucleus, the greater the attraction between the nucleus and the electrons. This means more energy is required to remove the electron, resulting in a higher ionization energy.
How are ionisation energies influenced by the electron shielding?
Electron shielding affects ionization energy by reducing the nuclear attraction on the outer electrons. The more inner shells of electrons an atom has, the greater the shielding effect, and the lower the ionization energy.
How are ionisation energies influenced by the electron sub shell when an electron is removed?
The energy of the orbitals increases from s to d, so the orbitals are filled in this order. For example, in magnesium, the large increase in ionization energy from the second to the third ionization energy indicates that the valence shell must contain only two electrons. This corresponds to moving from the 3s to the full 2p subshell.
Why does first ionisation energy increase across a period?
First ionization energy increases across a period on the periodic table because of the increase in nuclear charge and the decrease in atomic radius.
Nuclear charge: As you move across a period, the atomic number increases, which means the number of protons in the nucleus increases. This increases the nuclear charge.
Atomic radius: As you move across a period, the atomic radius decreases slightly. This is because the increased nuclear charge pulls the outer electrons closer to the nucleus.
Why does first ionisation energy decrease down a group?
First ionization energy decreases down a group on the periodic table because the distance between the nucleus and the outermost electron increases.
Increasing atomic radius: The atomic radius increases down a group, making the outermost electron farther from the nucleus.
Electron shielding: Shielding increases down a group, reducing the effect of the electrostatic forces of attraction.
Weaker attraction: The increase in distance and shielding outweighs the increase in the number of protons, making the attraction weaker.
Process of mass spectrometry
Ionization: A gaseous sample is ionized by knocking electrons off to create positively charged ions
Acceleration: The ions are accelerated so they all have the same kinetic energy
Deflection: The ions are deflected by a magnetic field based on their mass and charge
Detection: The ions hit a negatively charged detector plate, generating a signal proportional to the number of ions
How have the ideas of electronic configuration developed?
- Atomic emission spectra provides evidence for the existence of quantum shells
- Successive ionisation energies provide evidence for the existence of quantum shells and the group to which the element belongs
- First ionisation energy of successive elements provides evidence for electron sub-shells
How many electrons fill up the first four quantum shells?
2, 8, 18 and 32
What is an orbital?
A region within an atom that can hold up to two electrons with opposite spins
Shape of an s-orbital?
Spherical
Shape of a p-orbital?
Dumbbell
How many electrons occupy the s, p and d sub shells?
s = 2
p = 6
d = 10
How do electrons fill subshells?
Electrons fill subshells singly, before pairing up. Two electrons within the same orbital must have opposite spins
How to predict electronic configuration?
Using 1s notation and electrons within boxes (one arrow going up while the other arrow goes down within a single box)
How to classify elements?
Using s, p and d-block elements
What determines the chemical properties of an element?
Electronic connfiguration
What is periodicity?
A regularly repeating pattern of atomic, physical, and chemical properties with increasing atomic number.
As you go along period 2, does the melting point and boiling point increase or decrease?
As you move across period 2 of the periodic table, the melting point of elements first increases and then decreases.
As you go along period 3, does the melting point and boiling point increase or decrease?
For the metals in period 3, the melting and boiling points increase as you move from sodium to magnesium to aluminum. This is because the strength of the metallic bonds increases as the number of electrons and the charge on the nuclei increase. However, for the non-metallic elements in period 3, the melting points decrease from phosphorus to argon. This is because the melting points of these elements are low due to the weak van der Waals’ forces between the molecules. The strength of these forces depends on the size and number of electrons in the molecules.
As you go along period 2, does the ionisation energy increase or decrease?
Ionization energy increases as you move from left to right across period 2 on the periodic table. This is because the nuclear charge increases, which pulls the outer electrons closer to the nucleus. This makes it harder to remove an electron, so more energy is required.
In period 2, all the outer electrons are in 2s or 2p orbitals, which are roughly the same distance from the nucleus. The 1s2 electrons screen these orbitals.
Neon (Ne) has the highest ionization energy in period 2 because it is on the rightmost side of the period.
As you go along period 3, does the ionisation energy increase or decrease?
The ionization energy generally increases as you move across period 3 of the periodic table. The nuclear charge increases as you move across period 3, but the shielding of the outer electrons remains relatively the same. This means that the attraction between the nucleus and the outer electron increases, requiring more energy to remove the electron.
However, there are some exceptions to this general trend. Magnesium to aluminum: The ionization energy decreases between these two elements.
Phosphorus to sulfur: The ionization energy decreases between these two elements. This is because two of the 3p electrons in sulfur are paired, which reduces the force of their attraction to the nucleus.
