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Unit C Chemistry Flashcards

A concise lesson covering fundamental chemistry concepts: conservation laws, atomic models, scientific modeling, subatomic particles, isotopes, ions, and per...

19 cards~7 min
Unit C Chemistry Flashcards — Qwi
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1What law states that matter's mass remains unchanged during a chemical reaction?
Answer

Law of Conservation of Mass

It asserts that mass is conserved; reactants and products have equal total mass.
2This is now more commonly referred to as the Law of {{Definite}} Proportions.
Answer

Definite

3The Law of Multiple Proportions describes that compounds of the same elements combine in ratios of small whole numbers.
Answer

True

Dalton observed that when elements form more than one compound, the mass ratios are simple whole numbers.
4Difference between Dalton's first postulate and Thomson's Plum Pudding model?
Answer

Dalton → atoms are indivisible particles | Thomson → atoms contain electrons in a diffuse positive sphere

Dalton viewed atoms as solid, indivisible units; Thomson introduced internal structure with embedded electrons.
5List the four characteristics of a scientific model.
Answer

Simple, human‑created, testable, has limitations

Models aim to be as simple as possible, are constructed by people to aid understanding, must be testable, and acknowledge their limits.
6A tiny‑tiny‑tiny fraction of the massive positive alpha particles were deflected by small angles and about {{1 out of 20,000}} were deflected by more than 90°.
Answer

1 out of 20,000

7In the Rutherford model, most of an atom's mass is located in the electron cloud.
Answer

False

The mass is concentrated in the dense nucleus, while electrons contribute little mass.
8Which subatomic particle has a charge of +1 and a mass approximately 1 amu?
Answer

Proton

Protons carry a positive charge and have a mass close to one atomic mass unit.
9An isotope is defined as atoms of the same element with different numbers of {{neutrons}}.
Answer

neutrons

10How does the atomic number differ from the mass number?
Answer

Atomic number → number of protons | Mass number → protons + neutrons

Atomic number uniquely identifies the element; mass number gives the total nucleons.
11What is the common name for Group 1A elements?
Answer

Alkali metals

Group 1A, also called the alkali metals, are highly reactive metals.
12Elements in the same group have similar chemical properties.
Answer

True

Groups (columns) contain elements with comparable valence electron configurations, leading to similar behavior.
13The discovery of the neutron was credited to {{James Chadwick}} in 1932.
Answer

James Chadwick

14What does the symbol ^14_7N represent?
Answer

Nitrogen‑14 isotope (7 protons, 7 neutrons)

The superscript 14 is the mass number, the subscript 7 is the atomic number.
15How do isotopes differ from ions?
Answer

Isotopes → differ in neutrons, same charge | Ions → differ in electrons, charge changes

Isotopes keep the same elemental identity, while ions have altered electrical charge.
16The mass number of an isotope equals the number of protons in the nucleus.
Answer

False

Mass number equals protons plus neutrons.
17Who first coined the term “electron”?
Answer

J.J. Thompson

Thompson introduced the name in 1891 for the unit of electric charge observed in cathode‑ray experiments.
18The periodic table is arranged in order of increasing atomic {{number}}.
Answer

number

19What charge results on an atom when it loses 2 electrons?
Answer

2+

Losing two electrons gives the atom a +2 positive charge.

Fundamental Laws of Chemistry

The Law of Conservation of Mass states that matter's mass remains unchanged during a chemical reaction. Reactants and products have equal total mass, meaning mass cannot be created or destroyed.

The Law of Definite Proportions (often called the Law of Definite Proportions) asserts that a chemical compound always contains its component elements in a fixed ratio by mass.

The Law of Multiple Proportions describes that when two elements form more than one compound, the mass ratios of the elements are simple whole numbers. Dalton observed that these ratios are small, whole‑number multiples.

Atomic Models: From Dalton to Rutherford

John Dalton’s first postulate described atoms as indivisible, solid particles. In contrast, J.J. Thomson’s Plum‑Pudding model introduced internal structure: a diffuse positive sphere containing embedded electrons.

Ernest Rutherford’s experiments with alpha particles revealed that most of an atom’s mass is concentrated in a dense nucleus, not in the electron cloud. This corrected the earlier misconception that the electron cloud held the majority of the mass.

Characteristics of Scientific Models

Scientific models share four key characteristics:

  • Simple – they reduce complex reality to essential features.
  • Human‑created – they are constructed by scientists to aid understanding.
  • Testable – they must generate predictions that can be experimentally verified.
  • Limited – they acknowledge what they cannot explain.

Subatomic Particles and Their Properties

A proton carries a charge of +1 and has a mass of approximately 1 atomic mass unit (amu). Neutrons are neutral particles that differ in number among isotopes of the same element. Electrons have a charge of –1 and a negligible mass relative to protons and neutrons.

When an atom loses two electrons, it acquires a 2+ charge, reflecting a positive ion.

Isotopes and Ions

An isotope is defined as atoms of the same element that have different numbers of neutrons. For example, the notation ^14_7N represents a nitrogen‑14 isotope with 7 protons and 7 neutrons (mass number 14, atomic number 7).

Isotopes differ from ions in that isotopes vary in neutron count while retaining the same elemental identity and charge. Ions, on the other hand, differ in electron count, resulting in a change of electrical charge.

The statement that "the mass number of an isotope equals the number of protons in the nucleus" is false; mass number equals the sum of protons and neutrons.

Atomic Number vs. Mass Number

The atomic number indicates the number of protons in an atom and uniquely identifies the element. The mass number is the total of protons plus neutrons, providing the atomic mass of a specific isotope.

Periodic Table Organization

The periodic table is arranged in order of increasing atomic number. Elements in the same group (vertical column) share similar chemical properties because they have comparable valence electron configurations.

Group 1A elements are commonly known as alkali metals. These metals are highly reactive and readily lose their single valence electron to form +1 ions.

Historical Highlights

J.J. Thomson coined the term “electron” in 1891 after observing cathode‑ray phenomena. The discovery of the neutron was credited to James Chadwick in 1932, completing the picture of atomic structure.

In Rutherford’s scattering experiments, a tiny fraction of massive alpha particles were deflected by small angles, while about 1 out of 20,000 were deflected by more than 90°, indicating the presence of a dense, positively charged nucleus.

Review Questions

  1. What law states that mass is conserved in chemical reactions?
  2. Identify the missing word in "Law of {{Definite}} Proportions".
  3. True or false: Elements in the same group have similar chemical properties?
  4. Contrast Dalton’s atomic view with Thomson’s Plum‑Pudding model.
  5. List the four characteristics of a scientific model.
  6. What is the charge and approximate mass of a proton?
  7. Define an isotope in terms of neutrons.
  8. Explain the difference between atomic number and mass number.
  9. Who discovered the neutron and in what year?
  10. Interpret the notation ^14_7N.