1. The Precambrian is the earliest part of Earth's history, set before the current Phanerozoic Eon.
2.The Precambrian was originally defined as the era that predated the emergence of life in the Cambrian Period.
3. During the Precambrian era the earth started cooling and the outer edge of the planet solidified from molten lava to a solid crust. Water rained from the atmosphere and created oceans.
4. It is The first and longest subdivision of time for the earth.
5. The earth took form about 4.5 billion years ago. For the first 4 billion years of that time, the Earth was growing and changing.
6. he only multi-cellular life forms at the end of the Precambrian were in the oceans and included some groups that have survived until the present: jellyfishes and segmented worms.
7. The discovery of 3.85-billion-year-old marine sediments and pillow lavas in Greenland indicates the existence of liquid water and implies a surface temperature above 0 °C (32 °F) during the early part of Precambrian time.
8. The Precambrian encompasses the Archean and Proterozoic eons, which are formal geologic intervals that lasted from 4 billion to about 541 million years ago.
9. Precambrian rocks on most continents have revealed that additional primitive life-forms existed approximately 3.5 billion years ago.
10. The earliest evidence for the advent of life includes Precambrian microfossils that resemble algae, cysts of flagellates, tubes interpreted to be the remains of filamentous organisms, and stromatolites (sheetlike mats precipitated by communities of microorganisms).
F Orbitals
The n=4, l=3 orbitals are called f orbitals, and they’re difficult to describe. They have multiple complex features. For example, the n=4, l=3, m=0; m=1; and m=-1 orbitals are shaped like dumbbells again, but now with two donuts between the ends of the barbell. The other m values look kind of like a bundle of eight balloons, with all their knots tied together in the center.
D Orbitals
When n=3, then l can equal 2, and when l=2, m can equal 2, 1, 0, -1, and -2. The l=2 orbitals are called d orbitals, and there are five different ones corresponding to the different values of m. The n=3, l=2, m=0 orbital also looks like a dumbbell, but with a doughnut around the middle. The other four d orbitals look like four eggs stacked on end in a square pattern. The different versions just have the eggs pointing in different directions.
The atoms become larger, the intermolecular forces between the atoms become stronger and more energy is needed to overcome these forces. Hence, the boiling point of noble gases increases down the group.
What are noble gases?
- Group 18 of the modern periodic table consists of noble gases. Helium, neon, argon, krypton, xenon, and radon are noble gases.
- These gases are monoatomic and chemically inert under normal conditions and because of this they are also called inert gases. These gases are present in very small quantities in the atmosphere, and so they are also called rare gases.
Trends in Physical Properties of Noble Gases:
- Atomic Radii (Atomic size): As we move down the group from helium to radon the atomic size of Noble Gasses keeps on increasing. This is because when going down the group, the number of occupied shells with valence electrons increases.
- Boiling and Melting Points: As we move down the group, the boiling and melting point of the Noble Gasses increases due to the following reason:When moving down in the group, the atomic radius increases which results in the formation of a strong Van Der Waals force of attraction between the atoms.As to overcome the interatomic force of attraction which becomes stronger, it also requires more energy during melting and boiling.
- Density: All elements of group 18 have low densities. When going down the group, density increases as the atomic mass keeps on increasing.
- Ionization Energy: In the periodic table, As we move down the group the first ionization energy keeps on decreasing.
- Ionization Potential: When going down the group, the atomic radii increases which increases the attractive force and ultimately results in the increase of polarity and decrease in the ionization potential. This is because the larger atom of the group in the valence electrons are held together less tightly by the atom as they are situated far away from the nucleus.
To learn more about trends in noble gases:
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Answer:
The answer is oxygen and silicon
Explanation:
I took the test and it was right
