The Atom and The Periodic

Table of Elements

We can classify (arrange) elements in different ways:

• naturally occurring / made by scientists

• solid/liquid/gas

• metal/non-metal

Elements are pure substances that Elements are pure substances that cannot be broken down into any cannot be broken down into any simpler substance. Elements are the simpler substance. Elements are the basic building blocks of all matter.basic building blocks of all matter.

Compounds are any substances that Compounds are any substances that

are formed by the chemical are formed by the chemical combination of two or more elements combination of two or more elements and acts like a single substance and acts like a single substance

The Periodic Table is a system of The Periodic Table is a system of classifying all of the known elements classifying all of the known elements and was first developed by Dmitri and was first developed by Dmitri Mendeleev. Mendeleev.

Metals are found to the left of the Metals are found to the left of the zigzag line of the periodic table. zigzag line of the periodic table.

Nonmetals are found to the right of Nonmetals are found to the right of the zigzag line of the periodic table. the zigzag line of the periodic table.

Metalloids are metal or Metalloids are metal or metal-like elements found on metal-like elements found on both sides of the zigzag line. both sides of the zigzag line. Metalloids have properties of Metalloids have properties of both metals and non metals. both metals and non metals. EXAMPLES: Boron, Silicon, EXAMPLES: Boron, Silicon, Arsenic.Arsenic.

A vertical column of elements on the periodic table is called a group.

The elements in the same group of the periodic table have similar chemical properties.

•Periods are the horizontal rows

of elements on the periodic table. They do not have similar properties.

Every element is made up of very small particles called atoms.

+

–

Atoms of different elements have a different number called the atomic number.

Atoms have a very small, positively charged nucleus, with negatively charged electrons outside the nucleus in energy levels.

The nucleus of every atom (except hydrogen) contains two particles:

•Neutrons (no charge)

In energy levels outside the nucleus we find:

•Protons (positively charged)

•Electrons (negatively charged)

Atoms are neutral because the positive charge of the nucleus is equal to all of the negative charges of the electrons added together.

+

– • 11 electrons• 11 negative charges

• 11 positive charges• 11 protons

Atoms are neutral because the numbers of protons and electrons are equal - the opposite charges cancel.

Nuclide notation – how many protons, neutrons, and electrons are in atoms.

35

Mass number (protons + neutrons)

Cl17

Atomic number (number of protons)

As atoms have no charge, the number of electrons is the same as the number of protons. This atom has 17 electrons. (Electrons = Protons)

Scientists from our past.Scientists from our past.

Dmitri Mendeleev – developed the first Dmitri Mendeleev – developed the first periodic table in 1869. periodic table in 1869.

In 430 BC Greek Philosopher In 430 BC Greek Philosopher DemocritusDemocritus gave the name to the gave the name to the smallest piece of matter smallest piece of matter the the atomatom..

Joseph John “JJ” Joseph John “JJ” ThomsonThomson discovered discovered the electron in 1897. His model is the electron in 1897. His model is sometimes called the “plum pudding” sometimes called the “plum pudding” model. According to his model, the atom model. According to his model, the atom was made of a pudding-like positively was made of a pudding-like positively charged material throughout which charged material throughout which negatively charged electrons were negatively charged electrons were scattered.scattered.

In 1911 English scientist Ernest In 1911 English scientist Ernest RutherfordRutherford disproved Thomson’s model. disproved Thomson’s model. He reasoned that all of an atom’s He reasoned that all of an atom’s positively charged particles were positively charged particles were contained in the nucleus. The negatively contained in the nucleus. The negatively charged electrons were scattered outside charged electrons were scattered outside the nucleus around the atom’s edge. the nucleus around the atom’s edge. (credited for splitting the first atom) (credited for splitting the first atom) – Nucleus – the tiny, extremely dense, positively Nucleus – the tiny, extremely dense, positively

charged region in the center of an atom.charged region in the center of an atom.

In 1913 Danish Scientist, Niels In 1913 Danish Scientist, Niels Bohr,Bohr, discovered that electrons move or orbit discovered that electrons move or orbit around the nucleus. The current atomic around the nucleus. The current atomic theory states that electron clouds are theory states that electron clouds are where electrons are most likely to be in the where electrons are most likely to be in the space around the nucleus. space around the nucleus.

Subatomic ParticlesSubatomic Particles are are particles that are smaller than an particles that are smaller than an atom. The three main subatomic atom. The three main subatomic particles are particles are protons, neutrons, protons, neutrons, and electronsand electrons..

Electron CloudElectron Cloud is the space in is the space in which electrons are likely to be found which electrons are likely to be found (think of a beehive).(think of a beehive).

The four forces that account for the The four forces that account for the behavior of subatomic particles are:behavior of subatomic particles are:

1.1. Electromagnetic ForceElectromagnetic Force – a force – a force that can attract or repel the particles that can attract or repel the particles in an atom. This force holds the in an atom. This force holds the electrons around the nucleus.electrons around the nucleus. Example: If there were 2 protons (same Example: If there were 2 protons (same charge) the E.F. is repulsion. If there charge) the E.F. is repulsion. If there were 1 electron and 1 proton (opposite were 1 electron and 1 proton (opposite charge) the E.F. is attraction. charge) the E.F. is attraction.

2.2. Strong ForceStrong Force – opposes the – opposes the electromagnetic force of repulsion electromagnetic force of repulsion between protons. It binds protons between protons. It binds protons together to form the nucleus.together to form the nucleus.

3.3. Weak ForceWeak Force – responsible for a – responsible for a process known as radioactive decay. process known as radioactive decay. A neutron in the nucleus changes A neutron in the nucleus changes into a proton and an electron. into a proton and an electron.

44. . GravityGravity – the force of attraction – the force of attraction between all objects in the universe. between all objects in the universe. Of the four forces, it is the weakest Of the four forces, it is the weakest force. Why? The masses of the force. Why? The masses of the particles in atoms are so small, the particles in atoms are so small, the force of gravity within atoms is very force of gravity within atoms is very small.small.