Are There Particles Smaller Than the Atom

Atomic Structure Notes

Name: ______( ) Class: ______Date: ______

1. What is an atom?

An atom is the smallest unit of an element, having the properties of that element.

Each element consists of only one particular type of atom. In other words, the atoms of one element will be different from the atoms of another element.

2. Are there particles smaller than the atom?

Atoms are not like solid balls (Figure 1) as proposed by Dalton in 1803.

Figure 1: Dalton's model of the atom

In fact, atoms are made up of smaller particles known as subatomic particles.

3. Subatomic Particles

These subatomic particles comprise of

(a) proton (positively charged) (b) neutron (neutral - no charge) (c) electron (negatively charged)

Table 1 below provides additional data on proton, neutron and electron.

Particle Symbol Relative Mass Charge

Proton p 1

Neutron n 1

Electron e- 1/1836

1 Table 1 Thinking Time!

1. Why is the term "relative mass" used in the Table 1 rather than just mass?

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4. Counting Subatomic Particles.

(a) Proton Number

The number of ______in an atom is called the proton number. Proton number is also known as the ______Number.

(b) Nucleon Number

Nucleon number is the number of ______and ______in the nucleus of an atom. Nucleon number is also called the ______Number.

From the definition,

Nucleon (Mass) number = number of ______+ number of ______

5. Where can I find the proton number and nucleon number of an element?

Proton number and nucleon number of an element can be found together with the symbol of the 12 element in the Periodic Table (Figure 2). The carbon atom in symbol form is 6 C. It can also be written as carbon-12.

Figure 2

12 Question: How many protons, electrons, and neutrons are there in a 6 C atom?

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2 6. The Atomic Model

With reference to Figure 3:

(a) The centre of an atom is called the nucleus which contains the ______and ______.

(b) The electrons in an atom are arranged in ______(orbits) at different distances from the nucleus. The shell nearest to the nucleus is numbered 1, the second nearest is numbered 2 and so on.

Note: Shells are also called ______Figure 3

(i) 1st shell - ______electrons

(ii) 2nd shell - ______electrons

For the 1st 20 elements, the maximum number of electrons that can go into the third shell is 8. Advanced: For elements after calcium in the 4th period, their third shell can hold up to 18 electrons.

Some interesting facts...  The nucleus takes up less than 1% of the volume of a nucleus.  More than 99% of an atom is empty space occupied by rapid moving electrons.

Question

1. An atom can be described as an electrically neutral entity made up of a positively charged nucleus at its centre with negatively charged electrons moving around the nucleus.

(a) Why is the atom electrically neutral?

______

(b) Why is the nucleus positively charged?

______

7. How do I differentiate the atoms of one element from the atoms of another element?

All atoms of the same element have the same number of ______while those of different elements contain different number of ______.

8. Advanced: What are Isotopes?

Isotopes are atoms of the same element with different numbers of ______.

3 All atoms of the same element have the same number of protons. This means that isotopes of a certain element have the same proton number but different nucleon number. For instance, carbon has 3 isotopes: carbon-12, carbon-13 and carbon-14. 9. How are electrons being arranged in atoms?

(a) Electronic Structure & Electronic Configuration

Nitrogen-14 atom has 7 electrons. Two of its electrons will go into the 1 st shell, the remaining electrons will go into the 2nd shell (Figure 4). With 7 electrons, nitrogen has the electronic configuration of ______

Argon-40 atom has 18 electrons. Two of its electrons will go into the 1 st shell, 8 electrons will go into the 2nd shell, and the remaining 8 electrons will go into the 3 rd shell (Figure 5). With 18 electrons, argon has the electronic configuration of ______

Figure 4: Electronic Structure (Full Electronic Figure 5: Electronic Structure (Full Electronic Configuration) of Nitrogen-14 atom Configuration) of Argon-40 atom

(b) Valence Shell (Outer Shell)

The shell which is farthest from the nucleus and occupied by electrons is called the ______(outer shell). The electrons in the valence shell are known as ______(outer electrons). In a chemical reaction, only these valence electrons are involved in chemical bonding between atoms.

Often, only the valence electrons are drawn in the electronic structure. This is called the outer electronic structure. An example is shown in Figure 6 for the Nitrogen-14 atom.

Figure 6

Thinking Time!

How are the elements in the Periodic Table being arranged?

______

10. Formation of Ions

During chemical reactions, some atoms might lose/gain electron(s). Atom becomes an ______(charged particle) when it gains or loses electron(s).

Question: Why does an atom become a charged particle when it gains or loses electron(s)?

4 ______

______

(a) Formation of cations

When an atom loses one or more electrons, it becomes a positively charged particle called cation.

Lithium atom (Li) Lithium ion (Li+) 3 electrons 2 electrons 3 protons 3 protons Net charge: 0 Net charge: +1

In a lithium atom, there are 3 protons and 3 electrons. In a lithium ion, there are 3 protons and 2 electrons. Therefore, the lithium ion carries an overall positive charge of 1+ and is written as Li+.

(b) Formation of anions

When an atom gains one or more electrons, it becomes a negatively charged particle called anion.

Fluorine atom (F) Fluoride ion (F-) 9 electrons 10 electrons 9 protons 9 protons Net charge: 0 Net charge: -1

In a fluorine atom, there are 9 protons and 9 electrons. In a fluoride ion, there are 9 protons and 10 electrons. Therefore, the fluoride ion carries an overall positive charge of 1- and is written as F-.

Question for thought: Why do atoms become ions? (Note: this will be covered under chemical bonding)

______

5 (c) Exercise

1a. Fill up the blanks.

Charge of Element Name of Symbol of No. of electron No. of electron ion ion ion gained lost -2 Oxygen Oxide O2- Sulfur Sulfide S2- -1 Fluorine Fluoride F- Chlorine Chloride Cl- +1 Hydrogen Hydrogen H+ Lithium Lithium Li+ Sodium Sodium Na+ Potassium Potassium K+ +2 Beryllium Beryllium Be2+ Magnesium Magnesium Mg2+ Calcium Calcium Ca2+ Copper Copper (II) Cu2+ Iron Iron (II) Fe2+ +3 Aluminium Aluminium Al3+ Iron Iron (III) Fe3+

1b. Do metals generally form cations or anions? ______

1c. Do non-metals generally form cations or anions? ______

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