Question

1. what is the reason that scientists have changed the atomic model?
2. what determines the identity of an atom?
3. why is the overall charge of an atom neutral (zero)?
4. what happens to the motion of particles when energy is removed?
5. what happens to the distance of particles when energy is removed?
6. which state of matter has the highest particle movement?
7. which state of matter has the lowest particle movement?
8. what do elements in the same group share?
9. using the chart below answer the following questions:

a. hypothesis: the higher the temperature the faster the higher amount of salt will dissolve.
i. what is the independent variable?
ii. what is the dependent variable?
iii. what columns are the control variables?
iv. what two beakers should be looked at to get accurate results for this hypothesis?
v. why should the other two beakers not be used?

beaker	isopropyl alcohol (ml)	salt in kilograms (kg)	temperature of alcohol in °c	blending method
2	100	50	45	spoon
3	100	50	65	spoon
4	200	30	65	fork

Explanation:

1. As new experimental evidence and more advanced theories emerged, scientists refined the atomic model to better explain atomic - level phenomena.
2. The number of protons in the nucleus determines the identity of an atom, as it defines the element.
3. Atoms are neutral because the number of positively - charged protons is equal to the number of negatively - charged electrons.
4. When energy is removed, the motion of particles slows down as they have less kinetic energy.
5. When energy is removed, the distance between particles generally decreases as they move less vigorously.
6. Gases have the highest particle movement due to their high kinetic energy and lack of strong intermolecular forces.
7. Solids have the lowest particle movement as particles are closely packed and have limited freedom of movement.
8. Elements in the same group share the same number of valence electrons, which gives them similar chemical properties.

20.
i. The independent variable is the temperature of the alcohol as it is the variable being changed.
ii. The dependent variable is the rate at which the salt dissolves as it depends on the temperature.
iii. The columns for isopropyl alcohol volume, salt amount, and blending method are control variables as they are kept constant to isolate the effect of temperature.
iv. Beakers 1 and 2 should be looked at as they have the same amount of salt and blending method, with only the temperature varying.
v. Beaker 3 has the same temperature as Beaker 1 and doesn't help in showing the temperature - dissolution relationship, and Beaker 4 has different amounts of isopropyl alcohol and salt, introducing additional variables.

Answer:

1. New experimental evidence and advanced theories.
2. The number of protons in the nucleus.
3. Equal number of protons and electrons.
4. The motion of particles slows down.
5. The distance between particles generally decreases.
6. Gases.
7. Solids.
8. The same number of valence electrons.

20.
i. Temperature of the alcohol.
ii. Rate at which the salt dissolves.
iii. Isopropyl alcohol volume, salt amount, blending method.
iv. Beakers 1 and 2.
v. Beaker 3 has the same temperature as Beaker 1 and Beaker 4 has different amounts of isopropyl alcohol and salt, introducing additional variables.