Atoms

Structure of Atoms

Science Reading Q3/W4

Matter – anything that has volume and mass; occurs as elements, compounds, and mixtures

Our world is full of various substances we call matter. Matter is anything that takes up space (volume) and has mass. Take a look at the picture on the right. What kinds of matter do you see? The cars are made of solid matter such as metal frames and glass windows. Cars also need liquid matter to function, such as gasoline for fuel and oil for lubrication. The exhaust coming from the tailpipes is matter in the form of a gas. 

Atom – the smallest particle of an element, made of electrons, protons, and neutrons

The metal, glass, gasoline, and exhaust are composed of many different types of matter. For example, metal car frames are typically hard steel made from the elements iron and carbon, while the glass is a compound made of silicon and oxygen. The exhaust is a mixture of gases such as carbon dioxide. There are more than 100 different elements, each with its own type of atom. These atoms are the tiny particles that serve as building blocks of all matter.

Atom – the smallest particle of an element, made of electrons, protons, and neutrons

A bar of the element gold contains quadrillions of individual gold atoms. An atom is the smallest particle of an element that cannot be broken down without changing the properties of the element. One atom of gold is very small, too small to be visible. However, a single atom of gold has the same properties as every other gold atom. 

What are atoms made of?

Do all atoms have the same structure?

All atoms have the same general arrangement of particles, with protons and neutrons in the nucleus, or center, of the atom surrounded by a cloud of electrons. Scientists refer to this structure as the electron cloud model of an atom.

Multiple Choice

What is the model scientists refer to when looking at the structure of an atom?

• The electron cloud model

• The atom model

• The structure of our world model

• The theory model

Structure of Atoms

The location and charge of subatomic particles (particles inside of an atom) determine its structure. Protons, neutrons, and electrons differ from each other in their locations in an atom and their electrical charges. Electrical attractions between charged particles (ex: atomic nuclei and electrons) in matter explain the structure of atoms.

Structure of Atoms

Protons (shown as red spheres) are positively charged particles found in the nucleus of an atom. Since protons are the only charged particle in the nucleus, an atom’s nucleus is always positively charged. Atoms of each element contain a characteristic number of protons. In fact, the number of protons, or atomic number, determines the element.

Multiple Choice

Protons are negative and located outside of the nucleus.

• agree

• disagree

Structure of Atoms

For example, all nitrogen atoms have seven protons and, thus, an atomic number of seven. Sulfur atoms have 16 protons, while iron atoms have 26 protons.

Structure of Atoms

Neutrons (shown as yellow spheres) do not have an electrical charge. They are neutral. Neutrons are found in the nucleus of the atom.

Multiple Choice

Neutrons do not affect the overall charge of the atom.

• agree

• disagree

Structure of Atoms

Electrons (shown as blue spheres) are negatively charged particles. They travel within the electron cloud surrounding the nucleus. Electrons are constantly moving at nearly the speed of light.

Multiple Choice

Electrons make up most of the atom’s mass.

• agree

• disagree

Atomic Mass and Volume

Atomic mass is the average mass of all the protons and neutrons in an atom. The average atomic mass, in which P = number of protons and N = number of neutrons, is P + N. The unit for atomic mass is the atomic mass unit (amu). If an atom has three protons and four neutrons, its mass is 7 amu. Electrons are so small that they do not make a significant contribution to the mass of an atom. The nucleus of an atom is very dense, having much more mass than volume. The nucleus only takes up around 1% of the volume of the atom. Almost all the atom’s volume is taken up by the electron cloud.

Assumptions for Counting Subatomic Particles

If the number of protons equals the number of electrons, the atom does not have an electrical charge; it is neutral. In other words, the positives and negatives balance out.

If there are more protons than electrons, the atom is positively charged.

If there are more electrons than protons, the atom is negatively charged.

The number of neutrons in an atom does not affect the overall charge of the atom, because neutrons have no charge.

Multiple Choice

If there are more _________ than electrons, the atom is positively charged.

• protons

• neutrons

• electrons

Assumptions for Counting Subatomic Particles

Suppose a carbon atom has six protons and seven neutrons and is neutrally charged overall. How many electrons are in this atom of carbon? We know that the seven neutrons do not affect the overall charge of the atom. We also know that since the atom is neutral, it must have the same number of protons and electrons. Therefore, we can conclude that this carbon atom has six electrons.

Open Ended

Write 1 question you still have about the structure of atoms.

Open Ended

Write 2-3 things you want to remember about the structure of atoms.