Structure of the Atom
The tiny, dense, positively charged region at the centre of an atom.
What is the nucleus?
This subatomic particle has a relative mass that is considered negligible (approximately 1/1840 of a proton).
What is an electron?
The number of protons in an atom of an element; also equal to the number of electrons in a neutral atom.
What is the atomic (proton) number?
Define the term "isotopes."
What are atoms of the same element having the same number of protons but a different number of neutrons?
The maximum number of electrons that can occupy the first shell (closest to the nucleus).
What is 2?
The two subatomic particles found inside the nucleus.
What are protons and neutrons?
In a neutral atom, the number of electrons always equals the number of these particles.
What are protons?
The total number of protons and neutrons in the nucleus of an atom.
What is the mass (nucleon) number?
Since isotopes of an element have the same number of protons and electrons, this explains why they have identical ones of these.
What are chemical properties?
The maximum number of electrons that can occupy the second and third shells.
What is 8?
According to the nuclear model of the atom, electrons are arranged around the nucleus in these.
What are shells (energy levels)?
An atom that has lost or gained electrons, giving it an overall electric charge.
What is an ion?
An atom of chlorine has a mass number of 35 and an atomic number of 17. Calculate the number of neutrons.
What is 18? (35 − 17)
Two isotopes of hydrogen used in chemistry, besides ordinary hydrogen (protium), one containing 1 neutron and one containing 2 neutrons.
What are deuterium and tritium?
Write the electron configuration of a sulfur atom (atomic number 16).
What is 2,8,6?
State the relative charge and relative mass of a proton, a neutron, and an electron (all three, in a table format).
What is: proton (+1, mass 1), neutron (0, mass 1), electron (–1, mass 1/1840)?
Explain, in terms of subatomic particles, why an atom has no overall electric charge.
What is: the number of protons (positive) equals the number of electrons (negative), so the charges cancel out?
Chlorine has two isotopes: ³⁵Cl (75% abundance) and ³⁷Cl (25% abundance). Calculate the relative atomic mass of chlorine to one decimal place.
What is 35.5? [(35 × 75 + 37 × 25) ÷ 100 = 35.5]
Explain why isotopes of the same element have slightly different physical properties, such as density, even though their chemical properties are the same.
What is: isotopes have different numbers of neutrons, giving them different masses, and physical properties often depend on mass, whereas chemical properties depend on electron arrangement, which is identical?
Potassium has an atomic number of 19. Write its electron configuration, and explain why this arrangement places it in Group I of the Periodic Table.
What is 2,8,8,1 — it has only one electron in its outer shell, which is the defining feature of Group I elements?
Rutherford's gold foil experiment produced three key observations. State one observation and explain what it revealed about atomic structure.
What is: most alpha particles passed straight through (atom is mostly empty space); some were deflected at small angles (nucleus is positively charged); a few bounced straight back (nucleus is small, dense, and concentrated)?
A magnesium atom (Mg) forms a Mg²⁺ ion. Explain, in terms of subatomic particles, how this ion forms and why it carries a 2+ charge.
What is: the atom loses 2 electrons from its outer shell, so the number of protons (12) now exceeds the number of electrons (10), giving an overall charge of 2+?
Copper has two isotopes, ⁶³Cu and ⁶⁵Cu. Given that the relative atomic mass of copper is 63.5, calculate the percentage abundance of each isotope.
What is 75% ⁶³Cu and 25% ⁶⁵Cu? [Let x = % of ⁶³Cu: 63x + 65(100−x) = 6350 → x = 75]
Radioactive isotopes have applications in medicine and industry, but non-radioactive isotopes are chemically identical to the stable form of an element. Explain why isotopes cannot be separated using chemical methods, and suggest what property could be used instead.
What is: isotopes have identical electron configurations, so they undergo identical chemical reactions and cannot be separated chemically — but they can be separated based on their difference in mass (e.g. using a mass spectrometer)?
Sodium (2,8,1) and chlorine (2,8,7) react vigorously to form sodium chloride. Using electron configuration, explain why sodium is a highly reactive metal and chlorine is a highly reactive non-metal, and predict how a potassium atom (2,8,8,1) would compare in reactivity to sodium.
What is: sodium easily loses its 1 outer electron to achieve a stable full outer shell, while chlorine easily gains 1 electron to complete its outer shell — both driven by the tendency to achieve a stable electron arrangement; potassium would be MORE reactive than sodium because its outer electron is further from the nucleus (weaker attraction), making it easier to lose?