The AtomCambridge IGCSE Physics: Flashcards

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What is the basic structure of an atom?

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What is the basic structure of an atom?: An atom consists of a positively charged nucleus at the centre, surrounded by negatively charged electrons in orbit around it.
Describe the charge distribution in an atom.: The nucleus is positively charged, whilst the electrons orbiting the nucleus are negatively charged. In a neutral atom, the total positive and negative charges are equal.
What is an ion?: An ion is an atom that has gained or lost one or more electrons, resulting in a net electrical charge.
How is a positive ion formed?: A positive ion is formed when an atom loses one or more electrons. Since electrons are negatively charged, losing them leaves the atom with more protons than electrons, creating a net positive charge.
How is a negative ion formed?: A negative ion is formed when an atom gains one or more electrons. The gain of negatively charged electrons causes the atom to have more electrons than protons, creating a net negative charge.
What evidence does alpha particle scattering provide about the nucleus?: Alpha particle scattering by thin metal foils provides evidence that: the nucleus is very small compared to the atom; the atom is mostly empty space; the nucleus contains most of the atom's mass; the nucleus is positively charged.
Why do most alpha particles pass straight through the thin metal foil in the Rutherford scattering experiment?: Most alpha particles pass straight through because atoms are mostly empty space. The alpha particles rarely encounter the small nucleus, so they are not deflected.
What happens to alpha particles that pass close to the nucleus?: Alpha particles that pass close to the nucleus are repelled by the positive charge of the nucleus, causing them to be deflected from their original path.
What can be concluded about the size of the nucleus from alpha particle scattering?: The nucleus is extremely small compared to the overall size of the atom. Only a very small fraction of alpha particles are deflected, indicating the nucleus occupies only a tiny fraction of the atom's volume.
How does alpha particle scattering demonstrate that the nucleus is positively charged?: Alpha particles are positively charged. Those that approach the nucleus are repelled, which only occurs if the nucleus is also positively charged. Like charges repel, causing the deflection.
What does the large-angle scattering of some alpha particles tell us about the nucleus?: Large-angle scattering (including back-scattering) demonstrates that the nucleus contains most of the atom's mass. Only a highly concentrated, massive, positively charged centre could deflect alpha particles through such large angles.
Define the term 'electron'.: An electron is a negatively charged subatomic particle that orbits the nucleus of an atom. It is a fundamental particle with a very small mass.
Why are electrons able to orbit the nucleus?: Electrons are negatively charged and the nucleus is positively charged. The electrostatic attraction between opposite charges holds the electrons in orbit around the nucleus.
Explain what happens to an atom when it loses an electron.: When an atom loses an electron, it has fewer negative charges than positive charges. This results in a net positive charge, forming a positive ion (cation).
Explain what happens to an atom when it gains an electron.: When an atom gains an electron, it has more negative charges than positive charges. This results in a net negative charge, forming a negative ion (anion).