An atom is the smallest part of matter that consist of subatomic particles. Atom is made up of three different particles protons, neutrons and electrons. This particles are known as sub-atomic particles. Protons and neutrons are tightly packed together in the centre of an atom, forming the nucleus of the atom. Protons and neutrons are also known as nucleons. All atoms are electrically neutral. An atom contains an equal number of positively charged protons and negatively charged electrons. The positive and the negative electric charges cancel out exactly. Each protons carries 1 positive electric charge (+1) and has a relative mass of 1 . Each neutron carries no electric charge and has a relative mass of 1 . Each electron carries 1 negative electric (-1) and has a relative mass of 1/1840Electrons in an atom move around the nucleus in regions known as electron shells. Each electron shell can only hold a certain number of electrons. First shell which is closest to the nucleus, can hold a maximum of two electrons. Second, third and subsequent shells can hold up to eight electrons each. Th shell that is furthest from the nucleus is called the outer shell or the valance shell. The electrons in the shell are called valence electrons.
2. Draw the atomic structure of a sodium atom and a sodium ion....explain why you draw it this way.
An sodium atom has a proton number of 11. Thus the first shell consist of 2 electrons, second shell consist of 8 electrons and the valence shell consist of 1 electron. A sodium ion has a proton number of 10 as it loses 1 electons to achieve stability. This forms a positively charged ion.
3. Draw the atomic structure of a sulfur atom and a sulfide ion....explain why you draw it this way.
An sulfur atom has a proton number of 16. Thus the first shell consist of 2 electrons, second shell consist of 8 electrons and the valence shell consist of 6 electron. A sulfur ion has a proton number of 18 as it gains 2 electons to achieve stability. This forms a negatively charged ion.
4. Chlorine-35 atom and Chlorine-37 atom are called isotopes...Use these two examples to explain what is 'isotopes'
Chlorine-35 has a relative atomic mass number of 35.Chlorine-35 has 17 protons and 18 neutrons. As the nucleon number is 35 consisting of protons and neutrons (35n&p-17P=18n). Chlorine-37 has a relative atomic mass of 37.Chlorine-37 has 17 protons and 20 neutrons. As the nucleon number is 37 consisting of protons and neutrons (37p&n - 17p = 20n). They have the same number of protons but different number of neutrons. Chlorine-35 has 18 neutrons while Chlorine-37 has 20 neutrons. We know that isotopes are different atoms of the same element which have the same number of protons but different number of neutrons. Therefore, Chlorine-35 and Chlorine-37 are called isotopes as they are the different atoms of the same element, chlorine, only that they have different number of neutrons but same number of protons.
5. Sodium is a metal and sulfur is a non-metal....why we classify them this way??
PHYSICAL PROPERTIES
Group (I), (II), (III) of the periodic table are metals. Transition metals ( coloured metals ) are are also metals. Sodium is group (I). Therefore, it is a metal. Group (IV), (V), (VI), (VII), (VIII)/0 of the periodic table are non-metals. Sulfur is group (VI). Therefore, it is non-metal. Metals conduct electricity whereas non-metals do not conduct electricity. Sodium conduct electricity whereas sulfur do not conduct electricity.
CHEMICAL PROPERTIES
As we know, atoms of metals tend to lose valence electrons to form positive charged ions. Atom of non-metals tends to gain valence electrons to form negative charged ions. Metals have less than 5 electrons in the valence shell will lose electrons and while non-metals have more than 4 electrons in the valance shell will gain electrons. Sodium has a proton number of 11 . It has 1 valence electron, thus it loses 1 electron to achieve stabilitly. Sodium become a positively charged ion . Therefore, sodium is a metal. Whereas, Sulfur has a proton number of 16. It has 6 valance electrons , thus it gains 2 electrons to achieve stability and become a negatively charged ion. Therefore, Sulfur is a non-metal.
Acknowledgement
Textbook, notes, assessment book and my knowledge.
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Lee Hwee Leng 
