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Questions and Answers
Which statement accurately reflects Dalton's Atomic Theory regarding atoms?
Which statement accurately reflects Dalton's Atomic Theory regarding atoms?
What is the charge of an electron?
What is the charge of an electron?
What does the Law of Multiple Proportions state?
What does the Law of Multiple Proportions state?
Which of the following statements is true regarding the mass of protons and electrons?
Which of the following statements is true regarding the mass of protons and electrons?
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What important discovery did J.J. Thomson make in 1897 regarding atoms?
What important discovery did J.J. Thomson make in 1897 regarding atoms?
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Which observation from Thomson's experiment led to the conclusion that atoms can be divided into charged particles?
Which observation from Thomson's experiment led to the conclusion that atoms can be divided into charged particles?
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How is the atomic number of an element defined?
How is the atomic number of an element defined?
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In Chadwick's experiment, what was discovered?
In Chadwick's experiment, what was discovered?
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How are compounds defined according to Dalton's Atomic Theory?
How are compounds defined according to Dalton's Atomic Theory?
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Which of the following best describes isotopes?
Which of the following best describes isotopes?
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Study Notes
Atoms, Molecules, and Ions
- Atoms are extremely small particles making up elements.
- Atoms of the same element have the same size, mass, and chemical properties.
- Atoms of one element are different from atoms of all other elements.
- Compounds are constructed from atoms of more than one element.
- Compounds have a consistent relative number of atoms of each element.
- Chemical reactions involve the rearrangement of atoms.
- Atoms are neither created nor destroyed in chemical reactions.
Dalton's Atomic Theory
- Dalton's Atomic Theory (1808) described the fundamental nature of atoms:
- Elements are composed of extremely small particles called atoms.
- All atoms of a given element are identical in size, mass, and chemical properties.
- Atoms of one element are different from the atoms of all other elements.
- Compounds are formed when atoms of more than one element combine in a specific ratio.
- A chemical reaction involves the rearrangement of atoms; atoms are neither created nor destroyed.
Law of Multiple Proportions
- Compounds can have different proportions from the same element.
- This law explains how elements can combine in diverse ratios to form distinct compounds.
- For example, oxygen and carbon can combine in different ratios to form carbon monoxide (CO) and carbon dioxide (CO2).
Law of Conservation of Mass
- The total mass of the reactants in a chemical reaction is equal to the total mass of the products.
- States that matter is not created or destroyed in a chemical reaction.
- Matter is merely rearranged.
J.J. Thomson's Experiment
- Thomson's experiment involved cathode rays and electric fields to discover the electron.
- He found that cathode rays were composed of negatively charged particles.
- This finding contradicted the idea that atoms were indivisible.
- Thomson determined the charge-to-mass ratio of the electron.
Millikan's Experiment
- Millikan's experiment determined the charge of an electron.
- He used oil drops in an electric field to calculate the electron's charge.
- Combined with Thomson's data, this allowed calculation of the mass of an electron.
Radioactivity
- Some substances spontaneously emit radiation composed of different types of particles and energy.
- Three types of rays are alpha (α), beta (β), and gamma (γ) rays.
Rutherford's Gold Foil Experiment
- Rutherford's experiment involved firing alpha particles at a thin gold foil.
- Most particles passed through the foil, but some were deflected or scattered back.
- This suggested that the positive charge of an atom was concentrated in a small, dense nucleus.
The Nuclear Model of the Atom
- The atom consists of a dense, positively charged nucleus.
- Electrons orbit the nucleus in a much larger region of space.
- Atomic radius is much larger than the nuclear radius.
Chadwick's Experiment
- Chadwick's experiment discovered the neutron.
- Neutrons are uncharged particles with a mass similar to that of protons.
Subatomic Particles
- Electron (e⁻): Negative charge, very small mass.
- Proton (p⁺): Positive charge, larger mass than electron.
- Neutron (n⁰): No charge, larger mass than electron.
Atomic Number (Z), Mass Number (A)
- Atomic number (Z): Number of protons in an atom.
- Mass number (A): Number of protons + number of neutrons in an atom.
Isotopes
- Isotopes of an element have the same atomic number (Z) but different mass numbers (A).
- This difference comes from varying numbers of neutrons in the atoms.
The Modern Periodic Table
- Displays elements with similar properties grouped together in columns.
- Organized by atomic number.
Molecules and Molecular Compounds
- A molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds.
- A diatomic molecule consists of two atoms.
- A polyatomic molecule consists of more than two atoms.
Ions and Ionic Compounds
- An ion is an atom or group of atoms that has a positive or negative charge.
- Cations are positively charged ions.
- Anions are negatively charged ions.
Monatomic Ions and Polyatomic Ions
- Monatomic ions are ions containing only one atom.
- Polyatomic ions are groups of atoms that have a charge.
Do You Understand Ions?
- Calculation of protons and electrons in ions is based on the neutral atom's structure.
Formula of Ionic Compounds
- Electrical neutrality must be upheld in ionic compounds.
- Subscripts in a formula indicate the ratio of ions in the compound.
Naming Inorganic Compounds
- Ionic compounds: Metal + nonmetal, and ide suffix.
- Transition metals require Roman numerals for their charge.
- Molecular compounds: Nonmetal + Nonmetal, prefix rules.
Naming Acids
- Acids that contain hydrogen, oxygen, and another element (oxoacids) follow specific naming rules.
- Acids with other functional groups have different naming conventions.
Names and Formulas of Bases
- Bases are substances that release hydroxide ions (OH⁻) in water.
- The naming of bases follow common naming conventions.
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