Topic 1 Flashcards

Atoms, Elements & Compounds

Atoms, Elements & Compounds: read all 6 questions and answers

1. What is an atom?
   The smallest part of an element that can exist. All substances are made of atoms.
2. What is an element?
   A substance made of only one type of atom. Each element has a unique atomic number. There are about 118 known elements.
3. What is a compound?
   A substance formed when two or more different elements are chemically bonded together in a fixed ratio. Compounds can only be separated by chemical reactions.
4. How does a compound differ from a mixture?
   In a compound, elements are chemically bonded in fixed ratios and the compound has different properties from its constituent elements. In a mixture, substances are NOT chemically bonded and retain their individual properties.
5. What does a chemical formula tell you?
   It shows the types and numbers of atoms in a substance. For example, H₂O means 2 hydrogen atoms bonded to 1 oxygen atom.
6. Can compounds be separated by physical methods?
   No. Compounds can only be separated into their elements by chemical reactions, not by physical processes like filtration or distillation.

Mixtures & Separation Techniques

Mixtures & Separation: read all 9 questions and answers

1. What is a mixture?
   Two or more substances that are NOT chemically bonded together. They retain their individual properties and can be separated by physical methods.
2. When would you use filtration?
   To separate an insoluble solid from a liquid. The liquid passes through the filter paper while the solid particles are trapped (the residue).
3. What is crystallisation used for?
   To obtain a dissolved solid (solute) from a solution. Heat the solution to evaporate the solvent, then allow it to cool so crystals form.
4. What is simple distillation?
   A technique to separate a solvent from a solution. The solution is heated until the solvent evaporates, then the vapour is condensed back into a pure liquid in a condenser.
5. When would you use fractional distillation?
   To separate a mixture of miscible liquids with different boiling points. The liquid with the lowest boiling point evaporates first and is collected separately.
6. What is chromatography used for?
   To separate and identify mixtures of dissolved substances (e.g. Dyes or inks). Different substances travel at different rates up the paper, producing separate spots.
7. What does the Rf value tell you?
   The Rf value = distance moved by substance ÷ distance moved by solvent front. Comparing Rf values under identical conditions helps identify unknown substances, although different substances can share the same or similar Rf values in a given solvent.
8. How do you calculate an Rf value?
   Rf = distance moved by substance ÷ distance moved by solvent front. Example: spot moved 4.2 cm, solvent moved 6.0 cm → Rf = 4.2 ÷ 6.0 = 0.70. Rf values always fall between 0 and 1.
9. How can you tell if a substance is pure using chromatography?
   A pure substance produces a single spot on a chromatogram. An impure substance (mixture) produces two or more spots.

The Changing Model of the Atom

History of the Atom: read all 6 questions and answers

1. What was John Dalton's model of the atom (1803)?
   Dalton described atoms as tiny, solid, indivisible spheres. Each element was made of a different type of atom that could not be broken down further.
2. What did J.J. Thomson discover (1897)?
   Thomson discovered the electron using cathode rays. He proposed the 'plum pudding' model: a sphere of positive charge with tiny negative electrons embedded within it.
3. What did Rutherford's alpha scattering experiment show (1909)?
   Most alpha particles passed straight through gold foil (atom is mostly empty space), some were deflected, and a few bounced back (small, dense, positive nucleus). This disproved the plum pudding model.
4. How did Niels Bohr refine the atomic model (1913)?
   Bohr proposed that electrons orbit the nucleus in specific energy levels (shells) at fixed distances, rather than randomly. This explained the emission spectra of hydrogen.
5. What did James Chadwick discover (1932)?
   Chadwick discovered the neutron - a neutral particle in the nucleus with a relative mass of 1 and no charge. This completed our understanding of subatomic particles and explained why atoms had more mass than protons alone could account for.
6. Why has the atomic model changed over time?
   New experimental evidence led to revisions. Each model was replaced or refined when it could not explain new observations. This is how all scientific models develop.

Subatomic Particles & Isotopes

Subatomic Particles & Isotopes: read all 12 questions and answers

1. What are the three subatomic particles and their properties?
   Proton: mass 1, charge +1 (in nucleus). Neutron: mass 1, charge 0 (in nucleus). Electron: mass ≈ 0 (1/2000), charge −1 (in shells around nucleus).
2. What is the atomic number (Z)?
   The number of protons in the nucleus of an atom. This defines which element the atom is. In a neutral atom, protons = electrons.
3. What is the mass number (A)?
   The total number of protons + neutrons in the nucleus. Mass number = atomic number + number of neutrons.
4. How do you calculate the number of neutrons?
   Neutrons = Mass number − Atomic number (A − Z).
5. What are isotopes?
   Atoms of the same element with the same number of protons but different numbers of neutrons. They have identical chemical properties but different masses.
6. What is relative atomic mass (Aᵣ)?
   The weighted average mass of all the isotopes of an element, taking into account their relative abundances. It is relative to ¹²C (carbon-12 = 12).
7. How do you calculate Aᵣ from isotope data?
   Aᵣ = Σ(isotope mass × % abundance) ÷ 100. For example, Cl: (35 × 75 + 37 × 25) ÷ 100 = 35.5.
8. What is the approximate radius of an atom?
   About 1 × 10⁻¹⁰ m. The nucleus is about 1 × 10⁻¹⁴ m - roughly 10,000 times smaller than the atom itself.
9. A scientist observes a subatomic particle with a relative mass of approximately 1 and a positive charge. Which particle is this, and where would you find it?
   A proton, found in the nucleus of an atom.
10. Consider an atom of Carbon-12. What does the '12' represent, and how many of each subatomic particle does it contain?
    The '12' is the mass number (protons + neutrons). Carbon-12 has 6 protons, 6 neutrons, and 6 electrons.
11. A sample of chlorine contains both Chlorine-35 and Chlorine-37. If Chlorine-35 has 17 protons, how many neutrons does Chlorine-37 have?
    Chlorine-37 has 20 neutrons (37 - 17 = 20). Both isotopes have 17 protons because they are the same element.
12. A neutral atom of Oxygen (atomic number 8) gains two electrons. What is its new charge and electron configuration?
    It becomes an O²⁻ ion (charge of 2-) with an electron configuration of 2, 8. It now has 10 electrons but still 8 protons.

Electronic Structure

Electronic Structure: read all 6 questions and answers

1. What are electron shells?
   Energy levels around the nucleus where electrons are found. The first shell (closest) has the lowest energy, and each successive shell has higher energy.
2. How many electrons can each shell hold?
   1st shell: up to 2 electrons. 2nd shell: up to 8 electrons. 3rd shell: up to 8 electrons (at GCSE level).
3. What is the electron configuration of sodium (Na, Z=11)?
   2, 8, 1 - Two electrons in the first shell, eight in the second, and one in the third.
4. How does electronic structure relate to the periodic table?
   The number of occupied shells = the period (row). The number of electrons in the outer shell = the group number (for main groups). This links structure to chemical properties.
5. Why do elements in the same group have similar properties?
   Because they have the same number of electrons in their outer shell. The outer electron configuration determines how an element reacts.
6. What is the electron configuration of chlorine (Cl, Z=17)?
   2, 8, 7 - Chlorine is in Group 7 (7 outer electrons) and Period 3 (3 shells filled).

The Periodic Table & Groups

Periodic Table & Groups: read all 13 questions and answers

1. How did Mendeleev arrange the periodic table?
   In order of increasing atomic weight, grouping elements with similar properties into columns. He left gaps for undiscovered elements and predicted their properties - which were later confirmed.
2. How is the modern periodic table arranged?
   In order of increasing atomic (proton) number. Elements in the same group have the same number of outer shell electrons and similar chemical properties.
3. What are the properties of Group 0 (noble gases)?
   Full outer electron shells, so they are very unreactive (inert). They exist as single atoms (monatomic), have low boiling points, and boiling point increases down the group.
4. What are the properties of Group 1 (alkali metals)?
   Soft, low density metals with low melting points. They are very reactive - reactivity increases going down the group because the outer electron is further from the nucleus and easier to lose.
5. What happens when Group 1 metals react with water?
   They produce a metal hydroxide and hydrogen gas. For example: 2Na + 2H₂O → 2NaOH + H₂. The reaction gets more vigorous down the group (Li → Na → K).
6. What are the trends in Group 7 (halogens)?
   Non-metals that exist as diatomic molecules (F₂, Cl₂, Br₂, I₂). Reactivity DECREASES down the group. Melting and boiling points INCREASE down the group. Colour gets darker down the group.
7. What do the halogens look like at room temperature?
   Fluorine: pale yellow gas. Chlorine: green gas. Bromine: red-brown liquid. Iodine: dark grey solid (forms purple vapour when heated).
8. What is a halogen displacement reaction?
   A more reactive halogen displaces a less reactive halogen from a solution of its salt. For example: Cl₂ + 2KBr → 2KCl + Br₂ (chlorine displaces bromine).
9. What are the general properties of transition metals?
   Hard, strong, dense metals with high melting points. They can form ions with different charges, form coloured compounds, and are useful as catalysts.
10. How do metals and non-metals differ?
    Metals: conduct electricity, malleable, ductile, high density, form positive ions (lose electrons). Non-metals: poor conductors (insulators), brittle, low density, form negative ions (gain electrons).
11. What are noble gases used for?
    Helium: balloons and airships (low density, non-flammable). Neon: advertising signs (glows red-orange). Argon: filament lamps and welding (provides inert atmosphere).
12. Why does reactivity increase down Group 1?
    Going down the group, atoms have more electron shells. The outer electron is further from the nucleus and is more easily lost (weaker electrostatic attraction), making the atom more reactive.
13. How do you balance a chemical equation?
    Ensure the same number of each type of atom on both sides. Only change the large numbers in front of formulae (coefficients) - never change the small subscript numbers. Example: 2Mg + O₂ → 2MgO.