Question

atomic theory part 2- isotopes

quick review on early atomic theory:
an ______ is the smallest particle of an element that retains its identity in a chemical reaction. the existence of atoms as indivisible units of matter had been suggested 2,400 years ago, but these early ideas lacked experimental support and did not explain chemical behavior.

discovering subatomic particles:
john ____ , his atomic model marks the beginning of atomic theory. much of his atomic theory is accepted today, but we now know that atoms are __ . they can be broken down into smaller, more fundamental particles, called ____ particles, including electrons, protons, and neutrons.

in 1897, j.j ____ discovered __ , or negatively charged subatomic particles. thomson passed electrical current through electrodes in sealed tubes of gas. the electrons became charged, resulting in a glowing beam: cathode ray. __ rays are attracted to __ charged metal plates and are repelled by a negatively charged metal plate. since opposites attract and like charges repel, thomson deduced that cathode rays are beams of negatively charged particles he named ____ .

thomson concluded from his research that the mass of the negative charge was very small compared to the magnitude of the charge. thomson’s model can be thought of as a chocolate chip cookie or chocolate chips in ice cream. the “chips” represent the electrons evenly distributed.

image of a green sphere with blue dots (thomsons model) with blank labels

discovering the nucleus:
in ____ model of the atom, electrons travel around the nucleus like around the sun. rutherford experimented using __ ____ and alpha particles.

image of rutherfords model with blank labels

mass number:
when describing the structure of an atom, most of the mass comes from the protons and the neutrons. electrons have almost no mass (.0005). the total number of the ____ + ____ in an atom is called the mass number.

image of a bohr model-like diagram

check for understanding:
count the number of protons & neutrons to get the atomic number and mass number. put the corresponding values next to the carbon symbol - c.

isotopes: all atoms of an element have the same number of protons. however, atoms of the same element may have different numbers of ____ . isotopes are atoms that have the same number of protons but different numbers of neutrons. since isotopes of an element have ____ numbers of neutrons, they also have different mass numbers.

Explanation:

Quick review on Early Atomic Theory:

An atom is the smallest particle of an element that retains its identity in a chemical reaction. The existence of atoms as indivisible units of matter had been suggested 2,400 years ago, but these early ideas lacked experimental support and did not explain chemical behavior.

Discovering Subatomic Particles:

John Dalton - his atomic model marks the beginning of atomic theory. Much of his atomic theory is accepted today, but we now know that atoms are divisible. They can be broken down into smaller, more fundamental particles, called subatomic particles, including electrons, protons, and neutrons.

In 1897, J.J Thomson discovered electrons, or negatively charged subatomic particles. Thomson passed electrical current through electrodes in sealed tubes of gas. The electrons became charged, resulting in a glowing beam (cathode ray). Cathode rays are attracted to positively charged metal plates and are repelled by a negatively charged metal plate. Since opposites attract and like charges repel, Thomson deduced that cathode rays are beams of negatively charged particles he named electrons.

Thomson concluded from his research that the mass of the negative charge was very small compared to the magnitude of the charge. Thomson’s model can be thought of as a chocolate chip cookie or chocolate chips in ice cream. The “chips” represent the electrons evenly distributed (the “plum pudding model” - the green sphere with blue dots in the diagram represents the positive “pudding” with embedded electrons).

Discovering the Nucleus:

In the Rutherford model of the atom, electrons travel around the nucleus like planets around the sun. Rutherford experimented using gold foil and alpha particles (the diagram on the right: the central green sphere is the nucleus, the blue dots are electrons, and the orbits represent electron paths; the alpha particles were fired at the gold foil).

Mass Number:

When describing the structure of an atom, most of the mass comes from the protons and the neutrons. Electrons have almost no mass (0.0005 amu). The total number of the protons + neutrons in an atom is called the mass number.

Check for understanding:

For Carbon (C):

• Atomic number (protons) = 6 (all carbon atoms have 6 protons).
• Mass number = protons + neutrons. A common isotope of carbon (Carbon-12) has 6 neutrons, so mass number = \( 6 + 6 = 12 \). Thus, Carbon is represented as \( \boldsymbol{^{12}_{6}\text{C}} \).

Isotopes:

All atoms of an element have the same number of protons. However, atoms of the same element may have different numbers of neutrons. Isotopes are atoms that have the same number of protons but different numbers of neutrons. Since isotopes of an element have different numbers of neutrons, they also have different mass numbers.

Filling in the Blanks (from the worksheet):

1. Quick review: atom
2. Discovering Subatomic Particles: Dalton; divisible; subatomic; Thomson; electrons; Cathode; positively; electrons
3. Discovering the Nucleus: Rutherford; gold foil; (diagram labels: left - Plum Pudding Model (Thomson’s Model); right - Nucleus, Electrons, Electron Orbits)
4. Mass Number: protons; neutrons
5. Isotopes: neutrons; different

If you need help with specific blanks or further explanation, let me know!

Answer:

Quick review on Early Atomic Theory:

An atom is the smallest particle of an element that retains its identity in a chemical reaction. The existence of atoms as indivisible units of matter had been suggested 2,400 years ago, but these early ideas lacked experimental support and did not explain chemical behavior.

Discovering Subatomic Particles:

John Dalton - his atomic model marks the beginning of atomic theory. Much of his atomic theory is accepted today, but we now know that atoms are divisible. They can be broken down into smaller, more fundamental particles, called subatomic particles, including electrons, protons, and neutrons.

In 1897, J.J Thomson discovered electrons, or negatively charged subatomic particles. Thomson passed electrical current through electrodes in sealed tubes of gas. The electrons became charged, resulting in a glowing beam (cathode ray). Cathode rays are attracted to positively charged metal plates and are repelled by a negatively charged metal plate. Since opposites attract and like charges repel, Thomson deduced that cathode rays are beams of negatively charged particles he named electrons.

Thomson concluded from his research that the mass of the negative charge was very small compared to the magnitude of the charge. Thomson’s model can be thought of as a chocolate chip cookie or chocolate chips in ice cream. The “chips” represent the electrons evenly distributed (the “plum pudding model” - the green sphere with blue dots in the diagram represents the positive “pudding” with embedded electrons).

Discovering the Nucleus:

In the Rutherford model of the atom, electrons travel around the nucleus like planets around the sun. Rutherford experimented using gold foil and alpha particles (the diagram on the right: the central green sphere is the nucleus, the blue dots are electrons, and the orbits represent electron paths; the alpha particles were fired at the gold foil).

Mass Number:

When describing the structure of an atom, most of the mass comes from the protons and the neutrons. Electrons have almost no mass (0.0005 amu). The total number of the protons + neutrons in an atom is called the mass number.

Check for understanding:

For Carbon (C):

• Atomic number (protons) = 6 (all carbon atoms have 6 protons).
• Mass number = protons + neutrons. A common isotope of carbon (Carbon-12) has 6 neutrons, so mass number = \( 6 + 6 = 12 \). Thus, Carbon is represented as \( \boldsymbol{^{12}_{6}\text{C}} \).

Isotopes:

All atoms of an element have the same number of protons. However, atoms of the same element may have different numbers of neutrons. Isotopes are atoms that have the same number of protons but different numbers of neutrons. Since isotopes of an element have different numbers of neutrons, they also have different mass numbers.

Filling in the Blanks (from the worksheet):

1. Quick review: atom
2. Discovering Subatomic Particles: Dalton; divisible; subatomic; Thomson; electrons; Cathode; positively; electrons
3. Discovering the Nucleus: Rutherford; gold foil; (diagram labels: left - Plum Pudding Model (Thomson’s Model); right - Nucleus, Electrons, Electron Orbits)
4. Mass Number: protons; neutrons
5. Isotopes: neutrons; different

If you need help with specific blanks or further explanation, let me know!