bell work those of you who did not take your test friday need to sit in the back 2 rows. all others...
TRANSCRIPT
Bell Work
• Those of you who did not take your Test Friday need to sit in the back 2 rows. All others need to sit in the front 3 rows.
• How are elements arranged on the periodic table?
Physical Science – Lecture 57
The Periodic Table
Matter
• Matter is used to create atoms. • Atoms are used to create the elements. • Elements are used to create molecules.
Elements
• All elements are made of atoms. • The differ in weights and organization.• All atoms are built the same way.• Every element has electrons, protons, and
neutrons.
Elements on the Periodic Table
• The elements listed on the periodic table cannot be changed using any chemical method.
• Each element has a unique number of protons, giving each element its own atomic number.
Arrangement of Elements
• If you examine samples of iron and silver, you can't tell how many protons the atoms have.
• However, you can tell the elements apart because they have different properties.
• You might notice there are more similarities between iron and silver than between iron and oxygen. Could there be a way to organize the elements so you could tell at a glance which ones had similar properties?
The First Periodic Table
• Dmitri Mendeleev was the first scientist to create a periodic table of the elements similar to the one we use today.
• Mendeleev's original table was developed in 1869.
Mendeleev's Table
• When the elements were ordered by increasing atomic weight, a pattern appeared where properties of the elements repeated.
• This periodic table is a chart that groups the elements according to their similar properties.
Why is the Periodic Table Useful?
• Many elements remained to be discovered in Mendeleev's time.
• The periodic table helped predict the properties of new elements.
Mendeleev's Table
• The modern periodic table has over 100 elements.
• Mendeleev's table didn't have very many elements.
• He had question marks and spaces between elements, where he predicted undiscovered elements would fit.
Mendeleev’s Table
• Mendeleev found he could arrange the 65 elements that were then known in a grid or table so that each element had:
• 1. A higher atomic weight than the one on its left.
• 2. Similar chemical properties to other elements in the same column.
What about the other elements?
• In his table he noted gaps - spaces where elements should be but none had yet been discovered.
• Mendeleev could be said to have discovered germanium (which he called eka-silicon because he observed a gap between silicon and tin), gallium (eka-aluminum) and scandium (eka-boron) on paper, for he predicted their existence and their properties before their actual discoveries.
Discovering Elements
• The gaps in Mendeleev’s table helped him predict the existence of elements that had not been discovered yet.
Discovering Elements
• Elements with different numbers of protons are different elements.
• The gaps in atomic number on his table showed where new elements existed.
Adding to Today’s Table
• When you look at the modern periodic table, do you see any skipped atomic numbers that would be undiscovered elements?
Adding to Today’s Table
• New elements today aren't discovered. • They are made in labs. • You can still use the periodic table to predict
the properties of these new elements.
Properties and Trends
• The periodic table helps predict some properties of the elements compared to each other.
Properties and Trends
• Atom size, energy required to remove an electron, the ability to form a chemical bond, and other properties form patterns across and down the periodic table.
Today's Table
• The most important difference between Mendeleev's table and today's table is the modern table is organized by increasing atomic number, not increasing atomic weight.
Why was the table changed?
• Henry Moseley worked with Rutherford on the model of the atom.
• In 1914, Henry Moseley learned you could experimentally determine the atomic numbers of elements.
• Before that, atomic numbers were just the order of elements based on increasing atomic weight.
• Once atomic numbers had significance, the periodic table was reorganized.
Mendeleev’s Mistake
• They found that the atomic number (electric charge) is most fundamental to the chemical properties of any element.
• Mendeleev had believed chemical properties were determined by atomic weight.
• Moseley correctly predicted the existence of new elements based on atomic numbers.
Today’s Arrangement
• Today the chemical elements are still arranged in order of increasing atomic number (Z) as you go from left to right across the table.
• We also know now that an element's chemistry is determined by the way its electrons are arranged – by its electron configuration.