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General Chemistry: Atoms and Elements

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Termini in questo insieme (20)

  • What is an atom?

    An atom is the smallest identifiable unit of an element, composed of protons, neutrons, and electrons.

  • What does the word 'atom' mean and why is it significant?

    The word atom comes from the Greek atomos, meaning "indivisible." Atoms cannot be divided into smaller pieces and still retain their elemental identity.

  • Who first proposed the idea that matter is composed of small, indestructible particles?

    Leucippus and Democritus proposed that matter is made of small, indestructible particles called atoms that move randomly through empty space.

  • What are the three laws that led to the development of modern atomic theory?

    The law of conservation of mass, law of definite proportions, and law of multiple proportions were key to developing atomic theory.

  • State the law of conservation of mass.

    In a chemical reaction, matter is neither created nor destroyed; the total mass of substances remains constant.

  • Summarize John Dalton's atomic theory.

    Dalton's theory states: 1) Elements are made of atoms, 2) Atoms of an element are identical, 3) Atoms combine in whole-number ratios to form compounds, 4) Atoms cannot change into other atoms in reactions.

  • What did J. J. Thomson discover in his cathode ray experiments?

    Thomson discovered the electron, a negatively charged, low-mass particle present in all atoms.

  • What is the charge-to-mass ratio of the electron and how was it measured?

    Thomson measured the electron's charge-to-mass ratio by deflecting cathode rays with electric and magnetic fields.

  • What was the purpose of Millikan's oil drop experiment?

    Millikan's experiment measured the charge of a single electron by balancing gravitational and electric forces on charged oil droplets.

  • Describe the plum-pudding model of the atom.

    Thomson's model proposed electrons embedded in a positively charged sphere, like plums in pudding.

  • What did Rutherford's gold foil experiment demonstrate?

    It showed that atoms have a small, dense, positively charged nucleus and mostly empty space, disproving the plum-pudding model.

  • What are the three main points of Rutherford's nuclear theory of the atom?

    1) Most mass and positive charge in nucleus, 2) Electrons dispersed in empty space, 3) Equal number of protons and electrons for neutrality.

  • What is the role of neutrons in the atom?

    Neutrons are neutral particles in the nucleus with mass similar to protons, contributing to atomic mass but no charge.

  • List the three subatomic particles and their charges.

    Protons (+1 charge), Neutrons (0 charge), Electrons (-1 charge).

  • What defines the identity of an element?

    The number of protons in the nucleus, called the atomic number (Z), defines the element.

  • What are isotopes?

    Atoms of the same element with the same number of protons but different numbers of neutrons.

  • How is the mass number (A) of an atom calculated?

    Mass number A = number of protons + number of neutrons.

  • How is atomic mass of an element determined?

    Atomic mass is the weighted average of the masses of an element's isotopes based on their natural abundance.

  • What is the chemical symbol notation for isotopes?

    Isotopes are denoted as \(^A_ZX\), where X is the element symbol, A is mass number, and Z is atomic number.

  • Explain the significance of natural abundance in isotopes.

    Natural abundance is the percentage of each isotope present in a natural sample, affecting the element's average atomic mass.