Topic 1 - Key Concepts Of Chemistry - Atomic Structure Flashcards
Who published the first atomic theory and in what year?
John Dalton in 1803
Dalton’s theory laid the foundational principles of atomic structure.
What are the three main points of Dalton’s atomic theory?
- All substances are made of atoms.
- Atoms of the same element are exactly alike, and atoms of different elements are different.
- Atoms join with other atoms to make new substances.
Dalton’s theory was influential but later revised.
What did Dalton’s atomic theory state about atoms?
Atoms cannot be created, divided, or destroyed
This aspect was later challenged by discoveries of subatomic particles.
What significant discovery did J.J. Thomson make in 1897?
Atoms can be divided into smaller parts
This was a crucial revision to Dalton’s atomic theory.
What experimental method did J.J. Thomson use to discover electrons?
A cathode-ray tube
This experiment led to the identification of the electron.
What was the name of the model proposed by J.J. Thomson?
The ‘plum-pudding’ model
This model depicted electrons scattered throughout positively charged material.
What key experiment did Ernest Rutherford conduct in 1909?
He shot a beam of positively charged particles into gold foil
This experiment led to significant findings about atomic structure.
What observation did Rutherford make during his gold foil experiment?
Some particles were deflected to the sides and a few bounced straight back
This indicated the existence of a dense nucleus.
What did Rutherford conclude about the structure of the atom?
Most of the atom’s mass is found in the nucleus
This challenged the previous ‘plum-pudding’ model.
According to Rutherford’s model, what is the nature of the atom’s structure?
The atom is mostly empty space
This was a significant shift in understanding atomic structure.
Fill in the blank: In Rutherford’s model, electrons travel in _______ around the nucleus.
random paths
This was a new perspective on electron behavior.
What is the relative charge of a proton?
1
What is the relative charge of a neutron?
0
What is the relative charge of an electron?
-1
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
1/1836
Why do atoms contain equal numbers of protons and electrons?
Atoms are neutral; the charges on protons (+1) and electrons (-1) cancel each other out.
How does the size of the nucleus compare to the overall size of the atom?
The nucleus is very small compared to the overall size of the atom.
Where is most of the mass of an atom concentrated?
In the nucleus.
What is the meaning of the term mass number of an atom?
Mass Number = number of protons + number of neutrons.
What is unique about the number of protons in atoms of a given element?
Atoms of a given element have the same number of protons in the nucleus, and this number is unique to that element.
What are isotopes?
Different atoms of the same element containing the same number of protons but different numbers of neutrons.
How do you calculate the number of neutrons in an atom?
Number of neutrons = mass number - atomic number.
What is the atomic (proton) number?
The number of protons in an atom.
In a neutral atom, how do the number of protons and electrons relate?
The number of protons equals the number of electrons.
What are isotopes?
Atoms of the same element that have the same number of protons but different numbers of neutrons
Isotopes have different atomic masses due to the varying number of neutrons.
Why do some elements have relative atomic masses that are not whole numbers?
Because the relative atomic mass is an average calculated using the abundance of different isotopes
This averaging leads to non-whole number values even though atomic numbers and mass numbers are whole numbers.
How is the relative atomic mass (Ar) of an element calculated?
Using the abundance of different isotopes of the element
The calculation takes into account the different masses of the isotopes and their relative abundances.
What is the significance of a carbon atom in the context of atomic mass comparison?
A carbon atom with a mass number of 12 is taken as the standard for comparison
Its relative atomic mass is defined as 12.
What does Ar stand for?
Relative atomic mass
It is sometimes also referred to as R.A.M.
Fill in the blank: The atomic number and mass number are always _______.
whole numbers
True or False: The existence of isotopes means that all elements have whole number atomic masses.
False
Isotopes cause the average relative atomic mass to be a non-whole number.
What is the definition of relative atomic mass (R.A.M.)?
The average mass of an element’s isotopes, weighted by their abundances
Which isotopes are present in a sample of chlorine gas?
- Chlorine-35
- Chlorine-37
What are the proportions of chlorine-35 and chlorine-37 in the sample?
- 75% chlorine-35
- 25% chlorine-37
What equation is used to calculate the R.A.M. of chlorine?
R.A.M. = (mass of isotope-A x % of isotope-A) + (mass of isotope-B x % of isotope-B) / 100
Fill in the blank: The R.A.M. of chlorine can be calculated as _______.
(35 × 75) + (37 × 25) / 100
What is the calculated R.A.M. of chlorine in the sample?
35.5
True or False: The R.A.M. of chlorine is calculated using the masses of its isotopes and their respective percentages.
True
