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Chemistry Chapter 4 Flashcards
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Chemistry Chapter 4 Flashcards

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Questions and Answers

Who was Democritus?

An ancient Greek thinker who believed that matter could be divided into smaller particles until a basic particle was reached, suggesting the existence of atoms.

What are atoms?

The smallest particle of an element that retains both the chemical and physical properties of that element.

Who performed experiments to arrive at his Atomic Theory?

John Dalton

Which of the following are part of John Dalton's Atomic Theory? (Select all that apply)

<p>All matter is composed of atoms.</p> Signup and view all the answers

All of Dalton's theory is still true today.

<p>False</p> Signup and view all the answers

What are atoms made up of?

<p>Protons, neutrons, and electrons.</p> Signup and view all the answers

What is the actual mass of protons and neutrons?

<p>$1.67 \times 10^{-24}$ grams</p> Signup and view all the answers

Chemists use ______ comparisons of the masses of atoms.

<p>relative</p> Signup and view all the answers

What is the unit of comparison for atomic mass?

<p>Atomic mass unit (amu)</p> Signup and view all the answers

What does the atomic mass unit define?

<p>1/12 the mass of a carbon atom that contains six protons and six neutrons.</p> Signup and view all the answers

For all practical purposes, what is the mass of a single proton or neutron?

<p>1 amu</p> Signup and view all the answers

What is the symbol of an electron?

<p>e-</p> Signup and view all the answers

What is the relative electrical charge of an electron?

<p>1-</p> Signup and view all the answers

What is the approximate relative mass of an electron in amu?

<p>1/1840</p> Signup and view all the answers

What is the actual mass of an electron?

<p>$9.11 \times 10^{-28}$ grams</p> Signup and view all the answers

What is the symbol of a proton?

<p>p+</p> Signup and view all the answers

What is the relative electrical charge of a proton?

<p>1+</p> Signup and view all the answers

What is the approximate relative mass of a proton?

<p>1</p> Signup and view all the answers

What is the actual mass of a proton?

<p>$1.67 \times 10^{-24}$ grams</p> Signup and view all the answers

What is the symbol for a neutron?

<p>n^0</p> Signup and view all the answers

What is the relative electrical charge for a neutron?

<p>0</p> Signup and view all the answers

What is the approximate relative mass for a neutron?

<p>1</p> Signup and view all the answers

What is the actual mass of a neutron?

<p>$1.67 \times 10^{-24}$ grams</p> Signup and view all the answers

What is John Dalton's model of the atom?

<p>The atom was invisible and the smallest particle that could exist.</p> Signup and view all the answers

What shattered the idea of the invisible atom approximately 50 years after Dalton's death?

<p>The discovery of protons, neutrons, and electrons.</p> Signup and view all the answers

Who discovered the electron?

<p>Joseph J. Thomson</p> Signup and view all the answers

What model of the atom did Joseph J. Thomson propose?

<p>&quot;Plum pudding model&quot;</p> Signup and view all the answers

What does the plum pudding model describe?

<p>Negatively charged electrons embedded in a lump of positively charged protons.</p> Signup and view all the answers

What led to two hypotheses after the discovery of the electron?

<p>Atoms must contain something positively charged, and something that accounts for the mass.</p> Signup and view all the answers

Who figured out the mass of the electron?

<p>Robert Milikan</p> Signup and view all the answers

Who discovered the nucleus of an atom?

<p>Ernest Rutherford</p> Signup and view all the answers

What did Rutherford conclude from his Gold Foil Experiment?

<p>Most of the alpha particles passed through, indicating that mass and positive charge are concentrated in a small region called the nucleus.</p> Signup and view all the answers

Who proposed a model of the atom wherein electrons orbit around the nucleus?

<p>Niels Bohr</p> Signup and view all the answers

What is Bohr's model referred to as?

<p>&quot;Planetary model&quot;</p> Signup and view all the answers

In Bohr's analogy, what do the rungs of a ladder represent?

<p>The energy levels in an atom.</p> Signup and view all the answers

The amount of energy lost or gained by every electron is always the same.

<p>False</p> Signup and view all the answers

Unlike the rungs of a ladder, the energy levels in an atom are equally spaced.

<p>False</p> Signup and view all the answers

What is a quantum of energy?

<p>The amount of energy required to move an electron from its present energy level to the next higher one.</p> Signup and view all the answers

Who used the new quantum theory to describe the location and energy of an electron in a hydrogen atom?

<p>Erwin Schrodinger</p> Signup and view all the answers

What is the quantum mechanical model?

<p>A modern description of electrons in atoms that deals with the likelihood of finding an electron in a certain region of space around the nucleus.</p> Signup and view all the answers

What do we use today to describe atomic structure?

<p>Quantum mechanical model</p> Signup and view all the answers

What is the atomic number?

<p>The number of protons in the nucleus of an atom.</p> Signup and view all the answers

What is mass number?

<p>The number of protons plus the number of neutrons.</p> Signup and view all the answers

Since an atom is neutral, the number of protons equals the number of electrons.

<p>True</p> Signup and view all the answers

What determines what the atom is?

<p>The number of protons.</p> Signup and view all the answers

Atoms of the same element will always have the same number of ________ and ________.

<p>protons, electrons</p> Signup and view all the answers

Atoms of the same element can have a different number of _____________, and therefore, a different _____________

<p>neutrons; mass number</p> Signup and view all the answers

What are isotopes?

<p>Atoms of the same element that have different numbers of neutrons and a different mass number.</p> Signup and view all the answers

How do we distinguish atoms?

<p>Using chemical symbols.</p> Signup and view all the answers

What does hyphen notation indicate?

<p>The name of the element followed by the mass number.</p> Signup and view all the answers

How do you determine the number of protons from an atomic notation?

<p>By looking at the bottom left number.</p> Signup and view all the answers

How do you determine the number of electrons from an atomic notation?

<p>It is the same as the number of protons.</p> Signup and view all the answers

How do you determine the number of neutrons?

<p>Mass number - atomic number.</p> Signup and view all the answers

What do alpha particles consist of?

<p>The nuclei that have been emitted from a radioactive source.</p> Signup and view all the answers

What do beta particles consist of?

<p>Fast moving electrons formed by the decomposition of a neutron.</p> Signup and view all the answers

Why do alpha particles not travel very far?

<p>Because of their large mass and charge.</p> Signup and view all the answers

What can easily stop alpha particles?

<p>A sheet of paper or dead skin cells on the surface of your skin.</p> Signup and view all the answers

Why are alpha particles dangerous when ingested?

<p>They can penetrate soft tissue.</p> Signup and view all the answers

What distinguishes beta particles from alpha particles?

<p>Beta particles are much smaller and have half as much charge.</p> Signup and view all the answers

How are beta particles stopped?

<p>By aluminum foil or thin pieces of wood.</p> Signup and view all the answers

What are gamma particles?

<p>Electromagnetic energy.</p> Signup and view all the answers

How can gamma particles be stopped?

<p>By several feet of concrete or several inches of lead.</p> Signup and view all the answers

What does nuclear stability depend on?

<p>Its proton to neutron ratio.</p> Signup and view all the answers

For elements of low atomic number, below about 20, this ratio is _________. This means the nuclei have equal numbers of __________.

<p>one; protons and neutrons</p> Signup and view all the answers

Above atomic number 20, the stable nuclei have more ____________ than ____________.

<p>neutrons; protons</p> Signup and view all the answers

What is the band of stability?

<p>Contains all stable nuclei.</p> Signup and view all the answers

The stable ratio for lighter isotopes is represented as neutron/proton ratio=_____.

<p>1.0</p> Signup and view all the answers

The stable ratio for heavier isotopes is represented as neutron/proton ratio=_____.

<p>1.5</p> Signup and view all the answers

What occurs in region A?

<p>Unstable nuclei undergo beta decay.</p> Signup and view all the answers

What occurs in region B?

<p>Unstable nuclei convert a proton to a neutron.</p> Signup and view all the answers

What occurs in region C?

<p>Unstable nuclei undergo beta decay.</p> Signup and view all the answers

What is half-life?

<p>The time it takes for half of the nuclei in a radioactive sample to decay.</p> Signup and view all the answers

What does a longer half-life indicate?

<p>The more stable the radioisotope.</p> Signup and view all the answers

What happens in a chemical reaction?

<p>Atoms separate or combine without any changes to the nucleus, only electrons are involved, forming new compounds.</p> Signup and view all the answers

What happens in a nuclear reaction?

<p>The nucleus changes in composition, and new elements are formed by fusion or fission.</p> Signup and view all the answers

What is fusion?

<p>Two nuclei combine to form a new nucleus.</p> Signup and view all the answers

Fusion occurs on the ________ with _____________ combining to form ____________.

<p>sun; 2 hydrogens; helium</p> Signup and view all the answers

What is fission?

<p>Nucleus decays, releasing radiation.</p> Signup and view all the answers

What determines the chemical properties of a substance?

<p>Electrons</p> Signup and view all the answers

What determines the identity of a substance?

<p>Protons</p> Signup and view all the answers

What provides nuclear stability?

<p>Neutrons; they are the 'glue'.</p> Signup and view all the answers

When are elements 1-20 stable?

<p>When the number of protons and neutrons is approximately equal.</p> Signup and view all the answers

What do elements above 20 need to be stable?

<p>Increasingly more neutrons than protons.</p> Signup and view all the answers

What is true about elements above atomic number 83?

<p>They can't be stable and are radioactive.</p> Signup and view all the answers

What is the strong nuclear force?

<p>The force that holds the nucleus together and prevents protons from flying apart due to repulsion.</p> Signup and view all the answers

Study Notes

Key Historical Figures and Concepts of Atoms

  • Democritus: Ancient Greek philosopher suggesting matter can be divided into smaller particles called atoms.
  • John Dalton: Developed Atomic Theory through experimental evidence.
  • Atomic Theory Principles:
    • Matter is composed of atoms.
    • Identical atoms exist within the same element; different for different elements.
    • Atoms are indivisible and cannot be created or destroyed.
    • Atoms combine in whole-number ratios to form compounds.
    • Atoms rearrange during chemical reactions.

Atomic Structure

  • Atoms Composition: Composed of protons, neutrons, and electrons.
  • Mass of Protons and Neutrons: Each has an actual mass of approximately 1.67 x 10^-24 grams.
  • Atomic Mass Unit (amu): Defined as 1/12 the mass of a carbon atom with six protons and six neutrons, where 1 amu is taken to be the mass of a proton or neutron.
  • Electron Characteristics:
    • Symbol: e-
    • Relative charge: 1-
    • Approximate mass: 1/1840 amu, actual mass of 9.11 x 10^-28 grams.

Atomic Models and Discoveries

  • Dalton's Model: Proposed the atom as invisible, the smallest unit of matter.
  • Discovery of Subatomic Particles:
    • Joseph J. Thomson: Discovered the electron and proposed the "plum pudding model" of the atom.
    • Ernest Rutherford: Discovered the atomic nucleus via the "Gold Foil Experiment," concluding that most of an atom's mass is concentrated in a small nucleus.
    • Niels Bohr: Proposed the "planetary model," where electrons orbit the nucleus with fixed energy levels.
    • Erwin Schrödinger: Developed the quantum mechanical model, which predicts the probability of finding an electron in a given space around the nucleus.

Quantum Concepts

  • Energy Levels: Non-equally spaced; higher levels correspond to greater distances from the nucleus.
  • Quantum of Energy: The energy needed to move an electron to the next energy level.

Atomic Numbers and Isotopes

  • Atomic Number: Indicates the number of protons; determines element identity.
  • Mass Number: Sum of protons and neutrons; distinguishes isotopes, which are atoms of the same element with differing neutron counts.
  • Chemical Symbols: Utilized to represent various atoms, e.g., ^1H where 1 denotes mass number and atomic number.

Radioactivity and Nuclear Stability

  • Alpha Particles: Composed of 2 protons and 2 neutrons; low penetration ability, can be stopped by paper or skin.
  • Beta Particles: Fast-moving electrons; more penetrating and can be stopped by aluminum foil.
  • Gamma Rays: High-energy electromagnetic radiation; requires dense materials like lead or concrete for shielding.
  • Nuclear Stability: Relies on the proton/neutron ratio; stable nuclei exhibit different behavior based on atomic number.

Nuclear Reactions vs Chemical Reactions

  • Chemical Reactions: Involve electron interactions; do not affect the nucleus.
  • Nuclear Reactions: Changes in the nucleus, leading to new elements via fusion (combining nuclei) or fission (nucleus decay).
  • Half-life: Time taken for half of radioactive nuclei to decay; longer half-life indicates more stability.

Element Properties and Stability

  • Protons: Determine substance identity.
  • Neutrons: Provide stability in the nucleus.
  • Reactant Requirements: Lighter elements are stable with equal protons/neutrons, while heavier elements need more neutrons for stability.
  • Superfine Forces: Strong nuclear force holds the nucleus together, counteracting electrostatic repulsion among protons.

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Test your knowledge with these flashcards from Chapter 4 of Chemistry. Explore important concepts including the theories of Democritus and John Dalton, as well as the definition of atoms. Perfect for reviewing key terms and enhancing your understanding of atomic theory.

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