Question

What parts of Dalton’s atomic theory no longer agree with the current picture of the current picture of the atom? Provide an answer using at least 3 to 4 complete content related sentences in your own words.

If an element has 12 protons and 17 neutrons, how many electrons must it have?
Why are the atomic masses of elements usually decimal numbers? Provide an answer using 3 – 4 sentences in your own words.

Answer 1

Step-by-step explanation:

Dalton said that the atom was indivisible. We now know that it can be split up and it contains smaller particles such has protons, neutrons and electrons. Also he said that each atom of an element is the same. We now know that an element can exist as a number of isotopes with different numbers of neutrons.

It has 12 electrons . In the neutral atom the number of electrons = the number of protons.

The atomic masses are usually decimal numbers because most elements exist as a mixture of isotopes. For example hydrogen consists of hydrogen ( with no neutrons) , deuterium ( with 1 neutron) and tritium ( with 2 neutrons) and the atomic mass is 1.0079. The isotopes of an element are not usually given different names, like hydrogen, but are identified with their mass numbers eg Uranium@ U235, U238 and U239. (The mass number = sum of protons and neutrons in the nucleus).

Answer 2

Dalton's atomic theory states that atoms are indivisible. This has been proven through observation to be false: atoms can be divided into protons, neutrons and electrons. Dalton's theory also states that all atoms of an element are identical. This is also false because we know isotopes exist, and while they are still of the same element, they have different numbers of neutrons in their atomic nucleus.

It must have 12 electrons. The negative charge must equal a positive charge since the element has not been specified to be an ion. The reason atomic masses are usually decimal numbers is because electrons actually do contribute to the mass except in a very small amount. That amount is reflected by the decimal numbers you'll see in the atomic mass of an element.

I hope this helps!