Newton's Three Laws of Motion

First Law

The first law says that an object at rest tends to stay at rest and that a object in motion tends to stay in motion with the same direction and speed. If am ball is on top of a table motionless, and that there are no external force acting on it, it will never move. However, when the ball is in pushed by an external force towards the north, and that no other force is acting on it, it will never stop and never change direction. In the real world, this ball would sooner or later be stopped by friction between the ball and the table.

Second Law

Isaac Newton's second law is that the acceleration of an object is affected by the object's mass and the magnitude of force exerted. Similarly, the force applied on to the object can be calculated using the mass and the acceleration of the object. The formula is F=ma while F is the force applied, m is the mass of the object and a is the acceleration of the object. If you exert a similar force on to two object with different mass, both objects will accelerate differently.

Third Law

The third law is that for every action, there is an equal and opposite force. Forces are always found in pairs. For example, when a person is sitting on a chair, the person is exerting a downward force on the chair while the chair is exerting an upward force to support the person. This theory can also be proven when a rocket takes off. The rocket pushes down on to the ground with an enormous force, and the ground pushes the rocket up into the sky with the same amount of force.

Chemical Bonding

There are a total of 3 types of bonding, ionic bonding, covalent bonding and metallic bond (which we would be learning in Secondary 3).

An ionic bond is formed when a atom accepts or gives one or more of its valence electrons to one or more atoms. This way, all atoms must also have the atomic structure of a noble gas in order to form an ionic bond. One of the types of atoms must also be a metal while the other is non-metal. When an atom loses or gains electrons, it is no longer electrically neutral and is now called a ion. A negative ion is called a anion while a positive ion is called a cation.

An example of a ionic bond is between sodium and chlorine. With sodium being the metal and chlorine being the non-metal, sodium gives one of its valence electrons to chlorine and both of the atoms have a atomic structure of a noble gas. Both

Covalent bonding is formed when two or more atoms share their valence electrons with one another. Both atoms must be non-metal for covalent bonding to take place. After the bonding, all the atoms in the bond must have the atomic structure of a noble gas. When two atoms share their electrons and they only share one valence electron, both of the atoms form a single covalent bond. For example, two hydrogen atoms share one electrons with each other. Both electrons form a single covalent bond and both atoms also have the atomic structure of the element helium. When two atoms share two electrons, both atoms form a double covalent bond. Two atoms can also form triple covalent bonds when they share three electrons.

Extra: Metallic bonding is formed when a lot of metal atoms give up their valence electrons and become cations. These electrons move around between the metal ions and occupy the spaces between the ions. These electrons are called mobile electrons. Each of the positive ions are attracted to these electrons and it is this attractive force that holds the ion and electrons in the metal together.

Atoms

For the past few weeks, we have been studying about atoms. We studied about how atoms were first discovered, then we studied about what an atom is made of, finally we learnt about atoms bond together to create compounds.

History of Atoms

2500 years ago - Democritus said that matter is made up of tiny invisible particles called atoms.

1803 - Dalton's Theory: Atoms of same elements are alike, for example mass is the same, different elements have different types of atoms, atoms cannot be created, destroyed or changed and compounds are of two or more elements combined. Dalton's Theory forms the foundation of modern chemistry.

1877 - JJ Thomson's Model: Electrons are distributed among a mass of positive charges. JJ Thomson found out that an atom is a continuous mass of positive charges containing negative charges called electrons.

1911 - Rutherford's Model: Electrons are orbiting around a small, dense positively charged nucleus.

1915 - Bohr's Model: Electrons move around in a fixed orbit. An atom has a small and dense nucleus made up of of positively charged protons and electrically neutral neutrons. The negatively charged electrons move around the nucleus in fixed orbits. Only a certain number of electrons can be found in each shell.

1926 - Quantum Model: Electrons move around randomly and not in fixed orbits.

What are atoms made of?

Atoms are basically made up of electrons, protons and neutrons.

Electrons are negatively charged and they are the smallest of the three. They move around the nucleus, made up of protons and neutrons, in a random order. Electrons are found in "shells", each shell only able to hold a specific number of electrons. In the first shell, which is the shell nearest to the nucleus, it can only hold up to 2 electrons, while the second and third shell can hold 8. After the 40th element, the third shell can hold up till 18 electrons. The outermost shell is called the valence shell and the electrons inside it are called valence electrons. Only the valence electrons are used during bondings.

Protons are positively charged and they are found in the nucleus. There are the same number of protons as electrons, thus an atom is always electrically neutral.

Neutrons are also found in the nucleus. They have no charge.

Every atom has a mass number and a proton number. Mass number can also be said as nucleon number and proton number can also be said as atomic number. Mass number is the sum of the number of protons and neutrons while proton number is the total number of protons the atom has. These two information would be sufficient to find out all the numbers of electrons, protons and neutrons the atom has. For example, an oxygen atom has a mass number of 16 and proton number of 8. To find the number of neutrons, 16-8=8, thus we can tell that oxygen atom has 8 neutrons. The number of protons is already given and as the number of electrons are the same as the number of protons, oxygen has 8 protons and 8 electrons.

I also found out an easy way to remember the two phrases. As neutrons and protons are the heavier of the three parts, the mass is greatly influenced by the number of neutrons and protons. Thus, the mass number is the number of neutrons and protons. The proton number is also easy to remember because the name already tells me what it is referring to.

Even though atoms are quite confusing at first, I soon found out that it wasn't so hard to remember everything.