Question

4.3 atomic structure

1. experiments by j.j. thomson showed that atoms have

sketch the cathode ray tube experiment and label its components (late 1890s)
sketch the pudding model and label its components

1. rutherfords experiment (1911) discovered the nuclear atom

he used particles and thin gold foil to demonstrate:
atoms have a dense center of positive charge called the
the nucleus, which is at the center of the atom, consists of (positively charged) and (uncharged).
electrons move around the nucleus. sketch rutherfords model:

1. introduction to the modern concept of atomic structure

particle	relative mass	relative charge
proton	+1
	1839	none

1. neils bohr (1913) discovered that electrons in the atom can only occupy certain energy levels around the nucleus. sketch bohrs model:
2. isotopes are atoms with the same number of protons but different numbers of neutrons.

a particular isotope is represented by the symbol (_{z}^{a}x)
where a = number (sum of protons and neutrons)
z = atomic number (number of )
x =

Explanation:

Step1: Recall J.J. Thomson's experiments

J.J. Thomson's cathode - ray tube experiment showed that atoms have electrons. The plum - pudding model proposed by Thomson has electrons embedded in a sphere of positive charge.

Step2: Recall Rutherford's experiment

Rutherford used alpha particles and thin gold foil. He demonstrated that atoms have a dense center of positive charge called the nucleus. The nucleus consists of protons (positively charged) and neutrons (uncharged), and electrons move around the nucleus.

Step3: Recall particle properties

The relative mass of an electron is approximately $\frac{1}{1839}$ (but often approximated as 1 in relative terms compared to proton/neutron in simple models), and its relative charge is - 1. The relative mass of a proton is 1836 (approx. 1839 in some simple comparisons), and its relative charge is + 1. The particle with relative mass 1839 and no charge is the neutron.

Step4: Recall Bohr's model and isotope notation

Bohr discovered that electrons in the atom can only occupy certain energy levels around the nucleus. In the isotope notation $_{Z}^{A}X$, A is the mass number (sum of protons and neutrons), Z is the atomic number (number of protons), and X is the chemical symbol of the element.

Answer:

1. Electrons; Plum - Pudding
2. Alpha; Nucleus; Protons; Neutrons
3. - 1; 1839; Neutron
4. (Sketching of Bohr's model involves circular orbits of electrons around a central nucleus at specific energy levels)
5. Mass; Protons; Chemical symbol of the element