An atom consists of a small, dense nucleus (containing positively charged protons and neutral neutrons) surrounded by negatively charged electrons occupying defined energy levels (shells). The number of protons — the atomic number — defines which element an atom is, while the number of electrons in the outermost shell largely determines how that element behaves chemically. The periodic table's organisation reflects this: elements are arranged by increasing atomic number, with columns (groups) grouping elements sharing similar outer-shell electron configurations and therefore similar chemical properties.
Example
Sodium (atomic number 11) has an electron configuration of 2, 8, 1 — two electrons in its innermost shell, eight in the next, and just one lonely electron in its outermost shell — which it readily loses in chemical reactions, explaining why sodium is a highly reactive metal that forms compounds like sodium chloride (table salt) so easily.
Key terms
Atomic number:
The number of protons in an atom, defining which element it is.
Electron shell:
A defined energy level where an atom's electrons are located.
Questions
1. An atom's nucleus contains:
Protons and neutrons
Only electrons
Nothing at all
Only neutrons, with no protons
2. Electrons carry a charge that is:
Negative
Positive
Neutral, with no charge
Both positive and negative simultaneously
3. Protons carry a charge that is:
Positive
Negative
Neutral, with no charge
Both positive and negative simultaneously
4. Atomic number refers to the number of:
Protons in an atom
Only electrons, with protons uncounted
Only neutrons
Chemical bonds an atom can form
5. Electrons occupy:
Defined energy levels called shells
A single random location with no structure
The nucleus itself, alongside protons
No defined location at all
6. Elements in the periodic table are arranged by:
Increasing atomic number
Alphabetical order of their name
Random order with no pattern
Colour only
7. A group (column) in the periodic table contains elements with:
Similar outer-shell electron configurations
No relationship to each other at all
Identical atomic numbers
Only elements discovered in the same year
8. Sodium's electron configuration of 2, 8, 1 means it has how many electrons in its outermost shell?
1
2
8
11
9. Why does the number of outer-shell electrons largely determine how an element behaves chemically?
Outer-shell electrons are the ones most available to be gained, lost or shared in a chemical reaction with another atom
Outer-shell electrons never actually participate in any chemical reaction
Only the number of protons, never electrons, determines an element's chemical behaviour
Chemical behaviour has no connection to an atom's electron configuration
10. Why does sodium (with just one outer-shell electron) tend to be a highly reactive metal?
It readily loses that single outer electron in reactions, making it chemically eager to bond with other elements
Sodium never actually reacts with any other element under any circumstances
A single outer-shell electron always makes an element completely unreactive
The number of outer-shell electrons has no bearing on how reactive an element is
11. Why do elements in the same group of the periodic table (like sodium and potassium in Group 1) tend to share similar chemical properties?
They have the same number of outer-shell electrons, which is the main factor determining chemical behaviour
Elements in the same group always have completely different, unrelated electron configurations
Chemical properties are determined only by an element's atomic mass, never its electron configuration
Group membership in the periodic table has no genuine connection to shared chemical properties
12. Why is atomic number (rather than atomic mass) used as the defining property of an element?
The number of protons uniquely and consistently identifies an element, whereas atomic mass can vary between isotopes of the same element
Atomic mass is always identical to atomic number for every element, with no distinction
The number of protons in an atom can vary freely between atoms of the same element
Atomic number has no real connection to what actually defines an element
13. Why might chlorine (Group 17, with seven outer-shell electrons) tend to gain one electron in a reaction, rather than losing several?
Gaining just one electron completes its outer shell to a stable configuration, which is a much smaller change than losing seven electrons would require
Chlorine always loses seven electrons in every chemical reaction it participates in
The number of outer-shell electrons an atom has never influences whether it tends to gain or lose electrons
Gaining or losing electrons in a reaction has no connection to achieving a stable electron configuration
14. Why might an atom's overall electrical neutrality (equal numbers of protons and electrons) matter when explaining why atoms readily form ions by gaining or losing electrons?
Starting from a neutral, balanced state, gaining or losing electrons creates a charged ion, which can be energetically favourable if it results in a more stable electron configuration
Atoms are never actually electrically neutral to begin with, so this consideration is irrelevant to ion formation
Gaining or losing electrons always keeps an atom exactly electrically neutral with no resulting charge
The concept of electrical neutrality has no genuine connection to why or how atoms form ions
15. Why might an atom with a full outermost electron shell (like a noble gas) be especially unreactive compared to atoms with a partially filled outer shell?
A full outer shell is a stable configuration that has no strong tendency to gain, lose or share electrons in a reaction
A full outer electron shell always makes an atom highly reactive, more so than a partially filled one
Electron shell configuration has no bearing on how reactive or stable an atom is
Noble gases are actually the most reactive elements on the entire periodic table
16. Why might isotopes of the same element (atoms with the same number of protons but different numbers of neutrons) have very similar chemical behaviour but different physical properties like mass?
Chemical behaviour is driven mainly by electron configuration (determined by proton number), while physical properties like mass are affected by the differing number of neutrons
Isotopes of the same element always have completely different chemical behaviour from one another
The number of neutrons in an atom has no bearing on its mass or any physical property
Chemical behaviour and physical mass are always determined by exactly the same atomic property
17. Why might understanding electron configuration help predict the type of chemical bond (ionic or covalent) two elements are likely to form?
Elements likely to lose electrons (like metals) tend to bond ionically with elements likely to gain electrons (like non-metals), while similar elements often share electrons covalently
Electron configuration has no bearing on predicting what type of chemical bond might form between two elements
All elements always form exactly the same type of chemical bond regardless of their electron configuration
Ionic and covalent bonding are always completely indistinguishable from each other in practice
18. Why might the historical development of atomic models (from a solid sphere, to a nucleus-with-orbiting-electrons model, to the modern quantum-based model) reflect the scientific process of refining a model as new evidence emerges?
Each successive model was developed in response to new experimental evidence that the previous model couldn't adequately explain, showing how scientific understanding progresses
Atomic models have always remained completely unchanged and identical throughout the history of science
New experimental evidence has never actually led to any refinement or change in atomic models over time
The scientific process of refining a model based on new evidence has no connection to the historical development of atomic theory
19. Why might elements toward the left side of the periodic table (metals) tend to lose electrons in reactions, while elements toward the right (non-metals) tend to gain them?
Metals typically have few outer-shell electrons, making it easier to lose them and achieve a stable configuration, while non-metals have nearly full outer shells and more readily gain electrons to complete them
Metals and non-metals always behave identically in chemical reactions, with no distinguishing tendency to gain or lose electrons
The position of an element on the periodic table has no bearing on whether it tends to gain or lose electrons
Non-metals always lose electrons in reactions while metals always gain them, the reverse of the actual pattern
20. Why might scientists studying newly synthesised, super-heavy elements (with very high atomic numbers) use periodic table trends to predict their likely chemical properties before those properties can be directly tested?
Position within a group and period suggests a likely electron configuration and reactivity pattern, based on the well-established trends of elements above and near it on the table
Periodic table trends only ever apply to naturally occurring elements, never to newly synthesised super-heavy elements
The chemical properties of any element are always completely unpredictable and unrelated to its position on the periodic table
Predicting chemical properties from periodic table position has no scientific value or basis whatsoever
21. Understanding atomic structure and the periodic table mainly helps you to:
Explain how atomic structure determines an element's position and chemical behaviour in the periodic table
Assume the periodic table is arranged with no underlying scientific pattern
Ignore the connection between electron configuration and chemical reactivity
Treat atomic number and atomic mass as always exactly identical properties
Answer key (parent copy)
1. Protons and neutrons
2. Negative
3. Positive
4. Protons in an atom
5. Defined energy levels called shells
6. Increasing atomic number
7. Similar outer-shell electron configurations
8. 1
9. Outer-shell electrons are the ones most available to be gained, lost or shared in a chemical reaction with another atom
10. It readily loses that single outer electron in reactions, making it chemically eager to bond with other elements
11. They have the same number of outer-shell electrons, which is the main factor determining chemical behaviour
12. The number of protons uniquely and consistently identifies an element, whereas atomic mass can vary between isotopes of the same element
13. Gaining just one electron completes its outer shell to a stable configuration, which is a much smaller change than losing seven electrons would require
14. Starting from a neutral, balanced state, gaining or losing electrons creates a charged ion, which can be energetically favourable if it results in a more stable electron configuration
15. A full outer shell is a stable configuration that has no strong tendency to gain, lose or share electrons in a reaction
16. Chemical behaviour is driven mainly by electron configuration (determined by proton number), while physical properties like mass are affected by the differing number of neutrons
17. Elements likely to lose electrons (like metals) tend to bond ionically with elements likely to gain electrons (like non-metals), while similar elements often share electrons covalently
18. Each successive model was developed in response to new experimental evidence that the previous model couldn't adequately explain, showing how scientific understanding progresses
19. Metals typically have few outer-shell electrons, making it easier to lose them and achieve a stable configuration, while non-metals have nearly full outer shells and more readily gain electrons to complete them
20. Position within a group and period suggests a likely electron configuration and reactivity pattern, based on the well-established trends of elements above and near it on the table
21. Explain how atomic structure determines an element's position and chemical behaviour in the periodic table