Electron Arrangement and Bohr Diagrams Lesson 4

Review from Yesterday Protons- Heavy positively charged found in the nucleus Neutrons -are neutral particles that have the same mass as protons and are located in the nucleus Electrons- Negatively charged particles with almost no mass. They circle the nucleus at different energy levels. Nucleus contains protons and neutrons

nucleus

The atom - continued

The Nucleus The nucleus is a tiny part of the atom that contains protons and neutrons gathered together into a ball. The nucleus contains only a small part of an atom’s total volume. Depending on the atom, the region outside the nucleus of an atom is 10 000 to 50 000 times the diameter of the nucleus.

The Nucleus The nucleus contains 99.99% of the mass of the atom because protons and neutrons have much greater mass than electrons

Electrons Electrons exist in shells, or energy levels, surrounding the nucleus. The innermost shell can hold a maximum of two electrons. Each of the next two shells can hold up to eight. Electrons often exist in pairs in the shells. Electrons occupy more than 99.99% of an atom’s volume.

Electrons Electrons can move between energy levels. The outermost shell that has electrons in it is called the valence shell. Electrons in this shell are called valence electrons. Other shells containing electrons are called inner shells, and the electrons in them are called inner electrons.

Electrons The properties of elements are strongly affected by their valence electrons. When a shell becomes more than half- filled, the electrons begin to pair up, as shown in Bohr diagrams. Even though the negatively charged electrons repel each other, pairing helps electrons to get closer to the positive protons in the nucleus.

Patterns in the Arrangements of Electrons

Patterns in the Arrangements of Electrons A very important pattern in the arrangement of electrons is that elements in the same group have the same number of valence electrons.

Patterns in the Arrangements of Electrons Group 1: Atoms of hydrogen, lithium, and sodium each have one valence electron. These elements share some chemical properties with them because of their similar valence electron arrangements. They all form ions with a 1+ charge.

Patterns in the Arrangements of Electrons Group 18: Nobles gases have their valence shell completely filled with the maximum number of electrons that they can hold. The noble gases share many properties because their atoms all have filled valence shells, this makes them very stable.

Patterns in the Arrangements of Electrons The number of valence electrons is not only related to the physical properties of a group of elements. The number of valence electrons is also related to the ways in which atoms of elements combine to form compound

Bohr Diagrams Orbit # # of Electrons 1 2 8 3 4 18 To represent electron arrangements at various orbits we use Bohr diagrams. Each orbit has a set number of electrons. Orbit # # of Electrons 1 2 8 3 4 18

Every row in the period contains a shell Every row in the period contains a shell. The farther you move down the table the more shells you added to the diagram. H = 1 shell, Li = 2 shells, K = 3 shells.

Moving left to right on the periodic table adds valence electrons to the shells of that row. Na has 1 valence e-, Mg has 2 valence e-, Al has 3 valence e-, etc.

Drawing Bohr Diagrams Draw the Bohr diagram of Hydrogen N = A – Z N =

Drawing Bohr Diagrams Draw the Bohr diagram of Helium N = A – Z N =

Drawing Bohr Diagrams Draw the Bohr diagram of Lithium N = A – Z N =

Drawing Bohr Diagrams Draw the Bohr diagram of Beryllium N = A – Z N =

Drawing Bohr Diagrams Draw the Bohr diagram of Aluminum N = A – Z N =

Drawing Bohr Diagrams Draw the Bohr diagram of Argon N = A – Z N =

Draw the Bohr diagrams for the first 20 elements. – Hand in