Atomic Structure: Basic Concepts What is an atom? What are atoms made of? Where are protons located and what is their electrical charge? Where are neutrons located and what is their electrical charge? Where are electrons located and what is their electrical charge? Atom is the basic unit of matter Atoms are made of protons, neutrons and electrons. Protons are located in the nucleus of atom having positive electrical charge. Neutrons are located in the nucleus of atom having positive electrical charge Electrons are located in clouds outside nucleolus and have negative electrical charge.

What we think atoms look like…

The following statements are the main points of Dalton’s atomic theory. Dalton’s Atomic Theory 1.All elements are composed of tiny indivisible particles called atoms. 2.Atoms of the same element are identical and different from atoms of other elements. Atomic Structure: Basic Concepts

Dalton’s Atomic Theory 3.Atoms of different elements can mix together to form compounds. 4.Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms are never changed into atoms of another element as a result of chemical reaction.

Table of Elements A chemical element is a pure substance that is made of only one kind of atom. Ex: Carbon, Hydrogen, Oxygen, Nitrogen.

Carbon – a chemical element. 6 C Carbon Atoms are neutral (no electrical charge) because their number of protons is equal to the number of electrons. The number above the letter is the element’s atomic number, which is the same as the number of protons in its nucleus. The number of electrons in a neutral atom is the same as the number of protons.

The sum of the protons and neutrons in the nucleus is the mass number of that particular atom. * Mass number is also called atomic weight/atomic mass Masses The mass of a neutron is almost the same as the mass of a proton. However an electron is about 2,000 times lighter than a proton. Atomic Structure: Basic Concepts

Atomic Mass In order to have a simpler way of comparing the masses of individual atoms, chemists have devised a different unit of mass called an atomic mass unit, which is given the symbol u or amu. Atomic Structure: Basic Concepts Chemists have defined the carbon-12 atom as having a mass of 12 atomic mass units.

Isotopes of Carbon Nonradioactive carbon-12Nonradioactive carbon-13Radioactive carbon-14 6 electrons 6 protons 6 neutrons 6 electrons 6 protons 8 neutrons 6 electrons 6 protons 7 neutrons Isotopes are atoms with the same number of protons and electrons but different number of neutrons. Isotopes like carbon-14, C 14, can be used by scientists to determine the age of rocks and fossils.

Isotopes of Lithium

Electrons in Motion Niels Bohr ( ), a Danish scientist who worked with Rutherford, proposed that electrons must have enough energy to keep them in constant motion around the nucleus. Electrons have energy of motion that enables them to overcome the attraction of the positive nucleus. Atomic Structure: Basic Concepts

Electrons in Motion Bohr’s view of the atom, which he proposed in 1913, was called the planetary model. This energy keeps the electrons moving around the nucleus. Atomic Structure: Basic Concepts

The space around the nucleus of an atom where the atom’s electrons are found is called the electron cloud. The Electron Cloud Model These spherical regions where electrons travel may be depicted as clouds around the nucleus. Electrons themselves take up little space but travel rapidly through the space surrounding the nucleus. Atomic Structure: Basic Concepts

The Electron Cloud Model Atomic Structure: Basic Concepts

Electrons in Energy Level Each energy level can hold a limited number of electrons. How are electrons arranged in energy levels? The lowest energy level is the smallest and the closest to the nucleus. Atomic Structure: Basic Concepts

Electrons in Energy Level The second energy level is larger because it is farther away from the nucleus. It holds a maximum of eight electrons. This first energy level holds a maximum of two electrons. The third energy level is larger still and holds a maximum of 18 electrons. Atomic Structure: Basic Concepts

Energy Levels A hydrogen atom has only one electron. It’s in the first energy level. Atomic Structure: Basic Concepts

Electrons in Energy Level You can also use the periodic table as a tool to predict the number of valence electrons in any atom in Groups 1, 2, 13, 14, 15, 16, 17, and 18. The electrons in the outermost energy level are called valence electrons. All atoms in Group 1, like hydrogen, have one valence electron. Likewise, atoms in Group 2 have two valence electrons. Atomic Structure: Basic Concepts

Electrons in Energy Level An oxygen atom has eight electrons. Two of these fill the first energy level, and the remaining six are in the second energy level. Atomic Structure: Basic Concepts