The Atom Basic Chemistry

Atomic Structure Atoms contain 3 types of particles. Each particle has its own properties. An electron’s mass is so small, it is considered negligible (or the equivalent of zero.)

Atomic Structure The particles in an atom are arranged in a predictable, consistent manner. Nucleus: the center of the atom; contains protons and neutrons Electron Cloud: also called orbits or orbital shells; contains the electrons

Atomic Structure You can think of it as something similar to the solar system, where the sun is the nucleus and the planets are the electrons.

Atomic Structure In a “normal” atom the number of protons and electrons are equal. The electrons fill orbital shells in a predictable manner. The first shell holds up to 2 electrons before it is full. Shells 2 and 3 hold 8. Shell 4 holds up to 18. After that, don’t worry about it! (until you take chemistry)

Atomic Structure The electrons in the outermost shell are called valence electrons.

Atomic Structure Electrons fill shells from the inside out. 2 in the first, then 8 in the second, and so on. (It gets more complicated after the first few shells, but you don’t need to worry about that!)

Valence Electrons The electrons in the outermost shell are called the valence electrons. The number of valence electrons determines how the atom will interact with other atoms.

How Big is an Atom? https://www.youtube.com/watch?v=yQP4UJhNn0I

Ions Ions are charged atoms. They can be either positively charged or negatively charged. Positively charged ions have “lost” one or more electrons. Negatively charged ions have “gained” one or more electrons.

Ions Atoms like to have a full outermost electron shell. “Happy” ( proper term is STABLE) atoms have as many valence electrons as they can hold. Whether atoms will give up or gain electrons to form (stable) ions is determined by the number of valence electrons they have. A smaller number (1 or 2) number of valence electrons will form a positive ion. A larger number (6 or 7) of valence electrons will form a negative ion.

Ions Ions are written with their atomic symbol and the charge as a superscript.

Forming Ions Practice filling electron shells and then forming the corresponding ion. H (1); Li (3); O (8); K (19); Cl (17); Ca (20)

Noble Gasses Fill the electron shells and create ions for the following: He (2); Ne (10); Ar (18)

Noble Gasses Yeah, yeah. Mean trick. Noble gasses are already naturally stable atoms with full valence shells. Thus, they don’t form ions. Because they don’t form ions, they don’t interact with other elements. Yeah, they’re kind of snobs like that.

The Periodic Table The periodic table is a way of organizing elements by their properties. Elements are arranged by increasing atomic number (number of protons.)

The Periodic Table They are generally grouped into metals, nonmetals, and metalloids.

The column on the right is the noble gasses.

The Periodic Table You can also determine valence electrons (and, thus, ion charge) from the periodic table.

Information on the Table Each box is loaded with information, most you will need to know. Atomic number = number of protons Element symbol = shorthand form of writing Element name = sometimes not present Atomic mass = how much it weighs (average) From the mass, you can determine the number of neutrons (subtract atomic number from mass number)

Isotopes In each element, the number of neutrons may vary from atom to atom. REMEMBER! This CANNOT apply to protons. If you change the number of protons, you change the atomic number, and consequently have changed the element! Atoms of the same element with different numbers of neutrons are called isotopes.

Most elements have isotopes.

Isotopes Isotopes have: Atomic weight = # of protons + # of neutrons The same number of protons The same number of electrons Different number of neutrons Different atomic weight This is why the atomic weight is not an even number Atomic weight = # of protons + # of neutrons (Why not include electron weight?)

Chemical Bonds The electron cloud of an atom may have levels. Electrons in the outermost level, or shell, are called valence electrons. Atoms tend to combine with each other such that eight electrons will be in the valence shell. When atoms combine, a force called a chemical bond holds them together. A molecule is a group of atoms held together by chemical bonds.

Chemical Bonds, continued Chemical bonds form between groups of atoms because most atoms become stable when they have full valence shells. When atoms of different elements combine, a compound forms. A compound is a substance made of the bonded atoms of two or more elements.

Chemical Bonds, continued Ionic Bonding Atoms can achieve a stable valence level by losing or gaining electrons, resulting in a positive or negative charge. An ion is an atom or group of atoms that has an electric charge because it has gained or lost electrons. The attractive force between oppositely charged ions is an ionic bond. Why are these ions attracted to each other?

Visual Concept: Ionic Bonding Bond: Sodium to Chlorine Your Turn Bond: Sodium to Oxygen Potassium to Iodine Lithium to Fluorine Magnesium to Chlorine

Chemical Bonds, continued Covalent Bonding Another way that atoms bond is by sharing valence electrons to form a covalent bond. A water molecule, H2O, forms when an oxygen atom forms covalent bonds with two hydrogen atoms.

Covalent Bonding – Your Turn Chlorine + Chlorine 2 Carbon + 4 Hydrogen 3Hydrogen + Phosphorus Carbon + 2 Oxygen