The AtomThe Atom

Chapter 11 Notes and Review

By: Mr. Steffen

Dalton and Thompson started serious research on Dalton and Thompson started serious research on the atom. Dalton suggested that elements combine in the atom. Dalton suggested that elements combine in certain proportions because they are made of single certain proportions because they are made of single atoms. Thompson discovered that there are small atoms. Thompson discovered that there are small particles inside the atom. Thompson thought that particles inside the atom. Thompson thought that electrons were mixed throughout an atom, like the electrons were mixed throughout an atom, like the peanuts in “chunky” peanut butter.peanuts in “chunky” peanut butter.

John Dalton J. J. Thompson

Rutherford conducted experiments that showed both Thompson and Dalton had parts of it right.His experimentation led him to conclude that the atom was mostly empty space with a tiny part made of highly dense matter. Ernest Rutherford

Rutherford proposed that the center of the atom Rutherford proposed that the center of the atom was tiny, dense and positively charged called was tiny, dense and positively charged called the nucleus. The rays sent at the gold foil the nucleus. The rays sent at the gold foil would pass through the atom’s “empty” space and would pass through the atom’s “empty” space and bounce off of the densely packed nucleus.bounce off of the densely packed nucleus.

So atoms have a densely packed nucleus made So atoms have a densely packed nucleus made of protons (+) and neutrons (=), and a of protons (+) and neutrons (=), and a spacious outer area that holds electrons spacious outer area that holds electrons (-).(-).

Neils Bohrs later added that the electrons Neils Bohrs later added that the electrons moved around the nucleus in certain paths, or moved around the nucleus in certain paths, or energy levels. But electrons can jump from energy levels. But electrons can jump from path to path between levels, and each level path to path between levels, and each level can only hold a certain number of electrons.can only hold a certain number of electrons.

All atoms are different. Each had a different All atoms are different. Each had a different number of protons, neutrons and electrons. number of protons, neutrons and electrons. These combine to create all the matter around These combine to create all the matter around the Earth.the Earth.

THE PERIODIC TABLE OF THE PERIODIC TABLE OF ELEMENTSELEMENTSMendeleev started organizing the elements by atomic mass. Moseley refined the chart by atomic number. Moseley’s chart has been used ever since.

Atom – means not able to be divided; smallest particle an element can be divided into and still be the same substance

Elements combine in certain proportions based on mass to form compounds.

In 1803, scientists believed that atoms could not be broken down or divided into smaller parts. However, Thomson later (1897) found that they could be and further tests were done on atoms by other scientists.

Scientists found protons, neutrons, and electrons.

Nucleus – positively charged center that includes protons and neutrons; very, very dense

protons are positively charged and neutrons are neutral

A pinhead could be compared to a nucleus and a football stadium as the rest of the atom.

Electron Clouds – areas inside of an atom where electrons are likely to be found; the exact path cannot be predicted because they do not travel in exact paths

Protons – positive charge; mass is very small at 1.7x10-24

or 1 atomic mass unit, or amu *INSIDE the nucleusNeutrons – neutral charge; a little larger than a proton but so slight that it’s still considered to be 1 amu *INSIDE the nucleus

Electrons – negatively charged *mass is so small that they are not part of the total mass of the atom *takes more than 1800 electrons to equal the mass of 1 proton *the number of protons are ALWAYS equal to number of electrons in an element

*electrons travel on 4 levels OUTSIDE of the nucleusLevel 1 = 2 electrons Level 3 = 18 electrons Level 2 = 8 electrons Level 4 = 32 electrons Each level must be filled up before you can move to the next level.

Atoms have an overall neutral charge, but if the number of protons and electrons changes, the atom becomes an ion, which is a charged particle.

If an atom loses one or more electrons, it will have a positive charge. If an atom gains 1 or more electrons, it will have a negative charge because electrons have a negative charge.

The protons give an element its identity. For example, hydrogen has 1 proton, so that’s its atomic number.

15 P Phosphorus 31.0

15 is the atomic number, so you know phosphorus has 15 protons. Since protons are equal to electrons, there are 15 electrons. The mass is 31.0, which is the # of protons and # neutrons added together.

To find the number of neutrons, subtract the atomic # from the mass #. 31-15=16 neutrons inside the nucleus.

Phosphorus – 15 protons, 16 neutrons, and 15 electronsLevel 1 = 2 electrons, Level 2 = 8 elec., Level 3 = 5 elec.

(Draw your Phosphorus atom here)

Isotope – atoms with the same # of protons but different # of neutrons that share the same characteristics as the original element.

Each element has a limited # of isotopes found in nature. Some are unstable, which are called radioactive. They give off energy as they fall apart in nature.

Each element is its own “thing”. They have some things in common with other elements but each also has its own specific set of properties.

The Elements in all Their Glory